(I agree with your general idea and the rest of your comment.)
https://www.superlectures.com/guadec2013/sandboxed-applicati...
Unity came about with the Gnome 2 to 3 transition (and earlier versions of Gnome 3 were widely agreed to be a step backwards).
Upstart has a very different design philosophy than systemd. Hard to say its NIH when it was different tech.
NIH apparently means "not adopting whatever RedHat develops/supports".
Flatpak was known about and talked about before snaps, as another pointed out.
Upstart - that's fair, upstart was something new that didn't get replaced by systemd for a couple cycles.
Like it or not, Red Hat controls gnome which is a huge ecosystem. Your best bet for effecting change there is collaboration, not hacking together your own UI for yourself. I mean, sure they are free to do that, but the writing was on the wall before it even started.