Yes funlw65, you do have some good points.
QT might be a viable alternative but why do we want/need an alternative ? For me, the thing that makes FPC/Lazarus really great is that it produces a (usually) dependency free install.
Right now, on Linux we are all using GTK2 and, honestly, mostly happy about that but we are ignoring the future. Same as we did on the Mac, we wrote for Carbon right up until Apple started waving a big stick. Cocoa is now pretty good but no where near as stable as Carbon.
On Linux, we use GTK2, smug in the knowledge that Gnome will 'always' support it. Well, anyone tried to use the Lazarus SystemTrayIcon on (eg) a recent Fedora ? The Gnome developers decided that aspect of GTK2 was ugly (or something) and it no longer works in 'pure' gnome 3.28 or later.
Ubuntu had a similar AppIndicator for Unity (remember Unity ?) and still, at present, ship it. Last time I checked, Debian was not yet up to Gnome 3.28, been awhile....
My point is "we'll always support" is up to the supporter to define. And we may not like their definition !
My research prior to this post ? QT5 is not hard to get going using Ubuntu Repos but a form with one button idles at 100% cpu. The wki page on QT5 refers you to the readme.txt file that refers you to the wiki. GTK3 does not link, I guess there is binding library missing. The GTK3 wiki page is about 50 words long.
davo