We have a couple of options:

1. Migrate to Qt5
Pros: maybe better performance of the library, being always up-to-date, no problem "they'll drop our support"
Cons: More RAM usage, possible problems with the port being buggy

2. Stick with Qt4
Pros: no additional work required (apart from the UI creation)
Cons: Being more and more out-of-date, not receiving updates, need to find a stable commit.

3. Go for Gtk
Pros: Gtk support is still there, performance
Cons: Manpower that knows Gtk, how long will they support gtk2, Gtk and Mozembed issues. No examples (correct me if I'm wrong)

4. Switch to WebKit
Pros: We have QtWebkit in Qt4, good documentation
Cons: WebKit is unmaintained AFAIK, WebKit in Qt5 is probably newer.

5. Port Fremantle to Qt5
Pros: compat, possible performance
Cons: Whole lotta work! Really whole lotta... Impossible for two-men team

Please add your opinions and suggestions.