What is it that prevents the rest of the vim community from adopting neovim? From what I can observe, a great deal already have. But for the folks holding out, what is it that outweighs all that neovim has to offer?
Inertia. Such base programs basically need to go through the Debian packaging gauntlet if they want to succeed. What I mean by that is that generally they need to persuade distros to be anointed the "official" tool, i.e. Debian or Fedora would have to select Neovim as the new default text instead of Vim. Then you need a few years for the changes to trickle down everywhere: Debian -> Ubuntu-> Mint -> ..., Fedora -> RH…
You're probably right. However, I think it's more likely that the Linux distros drop Vim entirely and make Nano the default editor than that they replace Vim with Neovim.
The BSDs have nvi as the default editor, IIRC, so they won't need to change anything.