Heya Vespasianus!
I remember you from way back
We do have plans in incorporating most of InVain's submod into the main TLD branch. Not all will most likely make it, due to some of the scenes breaking the cutscenes. In regards to timeline, InVain is doing a lot of work in the main branch, so only he can answer when he can port most of his submod's scenes into the main branch.
Also, in regards to the steam update, the team's mandate is to make sure that all save games are compatible (i.e does not crash your game). We have done so continuously. Nevertheless, though your game may not crash, there may be changes that will not occur unless you start a new game. It doesn't prevent you from enjoying the mod, though
Lastly, InVain is doing some major balance changes to the main build, and unfortunately, we'd have to break savegame compatibility due to it. We will take this as an opportunity to create some placeholder items, so that we will (hopefully) not need to break compatibility again. This is good news, because I have not being adding new quests to the mod because of save game compatibility. Once we add the placeholders, I can start adding all our planned quests asap!
You can see our plans on our trello board
here
Apologies for answering in InVain's behalf

He'll probably chime in himself.