I don’t see much in the way of improvement. Someone posted another webengine-related crash less than 24 hours ago, and we can’t even use the current 6.4 release on Mac or Windows at the moment due to regressions.
You appear to be approaching this from a Linux-centric perspective, when we have the rest of the ecosystem to consider as well. 97% of Anki’s desktop userbase is on Windows/Mac, and GTK is generally considered to be inferior to Qt on those platforms.
There are also the mobile platforms to consider, with AnkiDroid accounting for a sizable portion of the userbase these days. Our traditional model has required them to port code and UI over to Android, and it’s led to them falling quite behind, and stalling adoption of newer functionality like the v3 scheduler. By sharing parts of the codebase and shifting parts of the UI to HTML, it will reduce duplicated effort, and allow us to make better use of the limited developer resources we have.