Since I've started using the system again, might as well give some feedback.
Would I use...
1. An offline client, allowing you to play campaigns against bots - Yes, and also just random games / cage matches / etc
2. A bot with a setting for different play styles - Probably not, just a stronger bot would be fine.
3. A strong bot. - Yes
4. Options for timed games - No, especially not if the game doesn't run more smoothly
5. Options for undo settings - Probably not, the current undo function works for me
6. Online mini-tournaments; the option to easily create one for you & your friends. - Maybe, if I had more friends that also played Dominion Online or if I decide to rejoin the Dominion League
7. Option to invite specific players to your table - Maybe, if I rejoin the League
8. More translations (to what language?) - No
9. Better animations when cards are gained/bought/played/... - No, especially not if the game doesn't run more smoothly
10. Better visualization of split piles, Archive/Crypt contents, Prince targets, ... - Yes, that would be great
10. Option to hide the log - No
11. Android app (or just improved compatibility?) - No
12. iPhone app (or just improved compatibility?) - No
13. Downloadable game logs - Yes, absolutely. It's rather annoying that there is no way to retrieve the log after finishing the game.
14. Improved moderation (dealing with chat abuse, slowplayers, ...) - No, mainly because I fear people will use it against me. I get accused of slowrolling fairly often, partially because I like to think my moves through and partially because the system is still pretty slow and laggy.
15. Tutorial on how to play Dominion - No
16. Tutorial on how to play dominion online. - Maybe just once to see if there's anything I missed
Honestly the main issue for me is still lag, although it might be less terrible than a year ago (or I've just gotten used to it, not sure).