Release Date Theory

Alright, here's my bit before I hopefully stop caring and just wait the coming weeks. Its going to come in thought snippets, but I think enough people will get what I mean.

Snowballs. Snow Ball. Snowfall.
Upside-down particles/ash fell onto Hawkins S4, like 'snow'.
Town infected, part of hive mind, part of bigger attack. Everyone 'cold', through perhaps susceptible to 'warmth'.
Church, holy day (or made unholy by Vecna's/Mindflayer's work).

The big byler event, the big 'snow' and 'church' event. The 'avalanche' of snow that leads to spring of requited love. The love that saves everyone and brings warmth to the 'upside down' that Will accidentally 'created' years ago (by theory), and makes it the 'rightside up' (the basic meaning of the episode title could mean something like the battle brought back to Earth, as well as the happy ending back on Earth, but I'm talking about beyond that).
The blue and yellow, the blue meeting yellow, the discovered warmth in Mike, the heart. (a purple color may be embraced by Eleven somehow, as she strikes out on her own and moves from Mike's yellow and Will's blue)

New Years release date is partially that stuff, to ring in the new chapter for everyone's lives, with newfound, perhaps surprising resolutions by everyone (including byler). An hour or more for the big conflict (the continuation of the Christmas cliffhanger), but under an hour for epilogue.