I don't think it would be too hard for Canonical to create some installed by default extensions and themes to make Unity users feel more at home in Gnome. The global menu is the only thing I can think of that would maybe be a little too tricky to be worth the effort.
In a way, maybe the year of the Linux Desktop was more convincing. At least people knew why they wanted that.
I like gnome3 visually, but some design choices by the gnome team I don't understand. While unity uses a global menu, which displays the menu items in several columns, The gnome global menu has 1 column, with for most apps a single entry (quit).
I'm fairly sure implementing unity/mac style global menus on GNOME can be done with an extension.
And if they don't contribute as much to the desktop, we'll probably see improvements in other areas such as performance.
BTW, I would go even further: will they still invest in the Snap package or they will do the same and go to a community oriented package system?
Try the Firefox Nightly for example: https://firefox-flatpak.mojefedora.cz/
In my understanding, GNOME Shell doesn't support Mir, only X11 and Wayland, so.
I have tried gnome shell in the past, but I still prever unity because of the global menu.
I might be a small minority, but I _like_ Unity 7. I have never used Unity 8, and I thought the Ubuntu phone was misspent effort, but wow. Now I have to figure out if there is a way to style Gnome to look like Unity 7.
I wonder what this means for Mir vs Wayland as well.