Mission System: Is this a Sandbox or a Themepark?

There is no reason why a mission system cannot exist in a game that allows for sandbox gameplay. Missions can give people extra / optional reasons to do things that provide pay-offs / rewards. Check out other space games such as Elite Dangerous, were you can decide to be an explorer, trader, miner without prompting, or you can undertake missions to do those things.

Also, they can provide a structure to the overall game environment. CIG have touted examples in the past whereby the generation of certain types of missions can end up creating scenarios and the creation of other missons (both player and system created).

In short, mission systems aren't exclusive to any one type of gameplay. It all comes down to how the system is implemented. History has shown that there are benefits and drawbacks to both total-sandbox and total-themepark type games. The best are those which can provide the benefits of both.

A lot of the missions will be triggered from in-game actions - they won't be predefined 'static' missions, as they would in a Themepark MMO.
 
That said, being a Sandbox game doesn't preclude having missions, or them being complex / having a story. It's more that Sandbox games offer more than just missions, whereas in most Themepark MMOs, missions are the key focus (along with levelling / grinding).
 
Separately, don't expect too much from 3.0. Yes, it's going to have the first iteration of Cargo - but it's only going to be the first iteration. It's not going to be full-featured and bug free, etc... From what I can tell, it's more that CIG are putting a few more objects in the game that are 'intended' to be moved (unlike BigBennies), and a simple interface to 'buy' and 'sell' them (which will automagically add / remove them from your ship).

the missions system gives us our basic professions..

the missions will all ask you to perform tasks along the lines of those careers listed on the image you linked.

this is an alpha, its the first iteration.

panties should remain unbunched during this process

I think I'll personally leave gameplay related decisions to people who work in the gaming industry.

"The first major career coming in 3.0 is Trading. Finally we have a real way to free-form accumulate wealth indefinitely"... Hmmmm, you can't buy ships with in game credit yet can you ? Do you not thing when release comes they gonna wipe everyone's assets except ships bought with real cash ? That was always my understanding, not sure why, maybe because of playing ED from beta and seeing how many credits people lost whilst grinding in the beta. Doesn't make sense to let people keep this in game currency as it's frequently accumulated from using bugs/xploits. So I wouldn't get too attached to your in game currency yet, or anything you bought in game.

Both, even themepark games become 'sandboxes' when you run out of things to do anyway. They are not mutually exclusive.

My read of it is that the foundation of the game is the professions and the dynamic mission system that puts player together competitively and cooperatively with the missions and any story driven content (assuming through mission) we might have being supplemental. So I see it heavily leaning towards a sandbox first for core game play with the writers continuously adding content over time to keep things interesting and perhaps appealing to a more diverse crowd.

Standard missions don't conflict with anything after all. You don't have to do them.

I've taken to calling it a hybrid sandbox, both for the inclusion of theme park style elements and because of the controls on the economy.

Missions are supplemental; they come secondary to careers and professions.

What?

Missions are the core of many professions.

Sure, you can be a trader that buys stuff from one station and sells it to another without a mission, this should be in 3.0. Playing it should be fun/engaging/whatever, but watching someone play it would be kinda dull for many (most?) people... You buy some stuff at a kiosk, wait a bit while it's loaded, fly from A to B, potentially get intercepted along the way, then repeat. Fun of your doing it, not so much if you're a passive observer who can easily do an infinite number of other things (ie you're sitting at your computer watching a YouTube video of them doing it).

Mercenary work, bounty hunting, personnel transport (though, that's kinda a hybrid of sorts, and they haven't gone into much detail recently) and more are going to be almost entirely mission based.

The more "free form" industry professions, Trading, Salvaging, and Mining, would likely take missions to reduce risk - basically ensure a specific return on part of their time/cargo while using the rest to speculate with, potentially getting higher returns - or losing their ass.

You spend 10-20 minutes getting to a good salvage field with a full crew complement in your Reclaimer... and it's gone because someone else got it. Now you're stuck with that hefty crew bill, and no salvage to sell. Getting a contract would ensure that you broke even, at least. Alternatively, the price of scrap (or ores in a miner's case) may collapse, but having that contract would lock you in at a specific return.

Being a crew member would be largely mission (contract) based as well.

It really depends on their implementation, to be honest. A sandbox game can work just fine with "missions" since they won't be something that triggers "progression" - there's simply no such concept, the game remains a sandbox which has multiple types of tools and the more these can be customised, the more they'll be able to provide the desired experience to different types of gamers. The missions system is mostly a tool to provide context-driven interactions with individual NPCs or their factions, as well as adding a feature that works similarly to side objectives for people that need direction to enjoy a game. As long as I don't have to see pop-ups with nagging reminders constantly and permanent on-screen icons of the place where I need to go, I get the type of experience I require from a sandbox, space sim kind of game. I've played X3 extensively, such a feature is exactly what that game was missing badly.

Unfortunately, it also sounds to me that they will spawn missions targeted for you when nothing happened for a long while. That sounds completely unimersive to me. I've seen this done in Elite: Dangerous and it's really badly done. These missions can still be context-driven. Economic and political factors in the system still decide the details, but the mission is spawned there because of my presence, not because it makes sense for an event to have occurred there specifically. I really hope they think this through and implement them in a believable way. Missions should be available to those who go search for them, not get in the way of normal gameplay. So, this is why I think it depends on their implementation, although the underlying idea is not necessarily problematic.

It's safe to think of missions as events. You could be hauling self purchased cargo to go sell it for a profit, only working for yourself, then you get a distress beacon. You choose to check it out, you find a ship wreck, or a pirate attack, or a message saying an escape pod was jettisoned which leads you to a planetary surface on which you find a survivor, or someone's remains ... you then can turn these in to whatever destination is requested and make some extra cash.

The availability of missions will be driven by the background economy simulation, but it doesn't seem that they will be required to enjoy, or thrive in the game. Although, earning positive reputation with certain companies/factions will open up lucrative opportunities.

Your mission should you choose to accept it.

That is the important aspect, we will be able to just do quick fast generated missions, or completely ignore them and create our own goals, activities, and focus. So it is a Sandpark or Themebox, providing as much or as little structure to our activities as we desire.