three things i’d try:
1. rethink the interface — there’s no way that current OS designs that’ve lasted 25 years are the end state of computing (this was the thesis of arc, btw!)
2. treat web apps and native apps the same. treat web docs and native docs the same.
3. new horizontal primitives. when you stop to think about it, it’s *so cool* that copy and paste actually works across every app. what’s the next clipboard, or the next url?
Same with KDE and some Freedesktop initiatives. There was even the effort to unify instant messaging services in Telepathy that was integrated with the system. Not to mention Nepomuk and semantic search.
We still have KIO to make remote or "virtual" resources appear as files and folders. And KRunner can still be used to provide some unified search but a few third party apps take advantage of it.
And sadly tabs in title bars to make windows behave more like browser tabs are gone.