You definitely are hearing things - but not real things. Firstly, there is no "sister" in this game - at least not for 5 years. Secondly, the coming update is the tech update; finally, the coming content updates after that are R(h)onda, Annie, & Judith focused.
I don't think you are remembering completely correctly - Yes, one of the (many) goals of the tech update was to make quicker turnaround possible for testing/etc (quicker being relative -- 1 day quicker is still quicker), but that doesn't mean updates will be released any sooner (or later) because of the tech update.
yes and no. The main story is finished (finding out about what happened to the MC's father) - but there are various other parts still to be completed. Also, people keep thinking that adult games made nowadays (particularly Visual Novels) are products which have definitive conclusions. This is a wrong conception. There is a current trend by developers that are creating these titles in a similar manner as episodic series as seen on TV/Cable/Netflix -- as long as there is enough audience interest and as long as the production team has the drive to keep developing, it is not inconceivable that a number of the titles could end up with 20+ years of content.
As far as I know, the school grades and the prom night are also part of the main quests. And almost all of that is still missing
School grades mean nothing. The prom night is a "main goal". The main story was to uncover who killed MC's notdad ....................... The other main goal is to gather enough $ to go to university (although that thing seems pretty meh when you can farm 1k a week)
DC won't magically draw an entire update within a week cause the codebase sux less, so the "speedup" if there's any will be in implementing said art into more bugfix builds and test them better/faster, without having to pray to RNGesus everytime for the game not to crap itself. The only "faster release" we could get is R(h)onda's, since the art for it (aside the lewds, that DC never streams so we dunno how far those are) was done last year. But then, the coder will probably die after the tech build and we'll still have to wait for him to either revive or for DC to get a new 1. Which then counters any speedups we might have gotten.
Keep hoping, it won't happen
Source for what ? Wincest got dumped in 2017. The next big update is indeed the tech build (for 2 years in dev now). And the routes after that are indeed R(h)onda's, Annie and Judith (once again known for 2 years, the tracker about those gets brought up every few posts as a meme). If you really want cold hard proof, check the wiki/main page links in the OP
Please don't go back a few pages and/or search, it would help me not want to punch kittens
