It will still be a long while until I add Explorers & Pirates to this, because before buying that expansion I would have to also buy a larger table. :P

I've managed to craft special rules that allow me to combine all mechanics from the following expansions and scenarios into that one Mega Catan experience. I will still level up this a bit more, so once that's done I will post here again with full updated rules to ask for your feedback as well. On this photo above I've added most importantly elements from Cities & Knights now.

So far this version combined the following into one game scenario:

\- Base Catan

\- Catan Cities & Knights

\- Catan Seafarers

\- Catan Traders & Barbarians with following scenarios:

 \- Scenario Traders and Barbarians from T&B

 \- Scenario Barbarian Attack from T&B

 \- Scenario Caravans from T&B

 \- Scenario Fishing from T&B

 \- Scenario Wonders of Catan from Seafarers

 \- Scenario Rivers from T&B

It keeps all special victory points like the one for the biggest amount of Knights, but as this is played with all development cards from all versions together the Knights from the base game and the Caravans scenario are given an extra ability to dispatch a Knight on the board to the castle hex (like standard Knighthood did), Knighthood now allows you to dispatch the Knight anywhere on the board (like standard Swift/Great/Black Knight) and the Swift/Great/Black Knight now additionally to its standard ability counts double for the purpose of getting the biggest amount of Knights special victory points.

Also the 3 Barbarians from the Traders and Barbarians scenario are now called Chieftans to distinguish them from standard barbarians and the knight figurines from C&K are renamed to soldiers to not confuse them with Knights.

Lastly the Barbarian Attack from C&K was renamed Pirate Attack to distinguish it from the other Barbarian Attack from the scenario Barbarian Attack from T&B.

Initial thoughts? I will share more soon. 

I've upgraded my setup again following your advice!