Maybe because it was not used anymore? I think Crapdroid has different "binding" with it, maybe only Fremantle and Harmattan used it and while they haven't been updated for ages, they dropped it? This are just speculations :P

If the work will be done in a proper way once, the annual maintenance wouldn't be that hard.

I vote a strong NO. Don't get me wrong I'm a big fan of Qt in general, but as long as we're still taking about GTK+Qt4 operaing system, I don't want to have another set of libraries loaded in RAM to open simple web page... I prefer to have more RAM and power for the webpage itself and GTK is sitting in the ram anyway on startup, so why load another stuff just to check the news or other silly stuff online? I would vote for consistency here (system components use GTK, so let's keep it up like it unless the lead of the team decides to change it altogether).

Just my useless 2 cents, I'm not even too active here lately, so if the active devs team has different oppinion, you don't even have to argue with me (in other words = if the person who will do it will do it in Qt5, but it will still work, I will be happy that it is done at all, after all it's their decision as they are the ones that put their precious time into it)