Linux

GNOME:

• support tags in all applications and have combined search for them (e.g. let me tag e-mails and files, and when I search for my tag the tagged emails and files show up) (AFAIK GNOME developers already said, this will never come, because it would confuse GNOME users. Apple and Apple users have this feature for years now.)
• Bring back F3 dual pane views in the file manager, having two windows side by side is not equivalent
• Integrate and polish dash to dock or dash to panel, I don't care which one just make it work perfectly OOTB.

Nothing. But once Wayland supports xscreensaver or vice versa I’ll switch.

bspwm - i do miss alt-tab from time to time.

I know there is a few sxkhd entries that sort of mimics it, but I miss something like gnome or cinnamon alt-tab

WMR support, I would ditch Windows in a heartbeat

Custom per-folder themes in Nemo with drag/drop templating like os/2 had. Extend to all apps, actually.

I want the ability to play all my steam, gog, origin and play natively, all this in a nice shiny cool looking desktop.

bonus if they add android app support