I do not agree with spoiler number 3. If you are in the no mans land at the beginning of a new chapter you can not upgrade any building if they are all maxed out. I was at the begin of the tech three of s&d level when the event started but am still not that far that I can upgrade any building.
Then you didn't read the whole thing. Specifically the quest would read "
Have XX level YY residences" and would be scaled based on the last
residence tech you unlocked, so there would never be a "no mans land" situation.
For example you could be at the start of chapter 10, and your quest would be to
HAVE 3 residences at level 23 which you unlocked in chapter 9. Once you unlock S&D residences the next quest would ask you to
HAVE 2 residences at level 25.
Best would probably be "
Have 6 level 23 residences
or upgrade 2 residences to level 23"
Obviously the numbers 6 and 2 can be tweaked and would be slightly different for each residence tech, but the idea remains the same.
This way you are either rewarded for progress you already made, or for progress you make.
Mainline (non-event) quests already trigger off unlocking techs, so it's certainly possible to tie event quests to residence techs as well.