My 2c. I have thought a lot about the UI so far, without posting, but re: this thread, and first OPs bullet points:
1) I completely agree. The four swipes from the edges of lockscreen and home screen are valuable "spots" for key functionality, and assigning all four to to the ambience switcher is a true waste. The panes/functions behind these four positions should be customizeable and the default should not be "ambience is everything". I for one rarely switches ambience (even if I understand the rationale and motivation from Jolla's side).
Patchmanager is OK, I use it, but in this respect it's far too little and these abilities should be built in.
2) Disagree, but...
3) Again, patchmanager work is under way. I agree that in principle the lockscreen should be locked. But
3a) I want more info there. There's just a lot of wasted empty space. E.g. I want my upcoming calender events and synced tasks there. (Btw: calender and tasks atm suck worse than a black hole.)
3b) some functions could be available on lock screen by pulls, e.g. each notification could accept a sideways pull to open corresponding app. This would be somewhat consistent with the homescreen-"tiles"-sideways-pull-functions.
4) Disagree. As long as the transition does not add more than (tens of) milliseconds to the actual load time, I really like it.

Couldn't agree more. This is a complete PITA. just remembering half-typed messages across windows/sessions, is a must (like N900 had always). Instead of separate windows for each chat: Perhaps an "active chats" switching mechanism that was faster than the go back-find other chat-tap way of today? (on a bigger screen this would be a sidebar.).