One potential problem is if Gnome make breaking changes, it's hard for Canonical (or anyone) to use it as a base for their own UI. I've not experienced this fir

One potential problem is if Gnome make breaking changes, it's hard for Canonical (or anyone) to use it as a base for their own UI. I've not experienced this first-hand, since I haven't used Gnome or written GTK+ apps since the 2.x days, but judging by what I've seen online they like to break APIs at each release, drop working features if/when their opinions change, and be semi-hostile to any use-case other than their own default settings ("brand"), e.g. https://igurublog.wordpress.com/2012/11/05/gnome-et-al-rotting-in-threes/ https://igurublog.wordpress.com/2012/11/05/gnome-et-al-rotti... https://davmac.wordpress.com/2016/07/05/why-do-we-keep-building-rotten-foundations/ https://davmac.wordpress.com/2016/07/05/why-do-we-keep-build... I suppose Canonical are big enough to have their needs taken into account, unlike other app authors.