I suspect most users could download neovim, symlink their .vimrc/.nvimrc, alias vim=nvim and not be able to tell the difference.
I'm a very heavy vim user and have been using neovim for a while now. It causes me zero issues even following git master, but I can definitely notice improvements.
I hope there's more that than. I personally don't use any plugins for which this is a problem. Not doubting those plugins exist, but apparently you can get by as a Vim user without them.
I see potential for the embedding api. If I could run Vim on a server and connect to it from a web app I would find that to be very compelling. Maybe there are other features that will set it over the top, but I'm still waiting.
Async support is a big deal for a lot of people though (and it's neovims original raison d'etre). For example, not having :make (well, :Neomake) block on compile is pretty significant by itself. Under the hood getting real async tasks required/requires a ton of rewriting because of how Vim was architected. Those changes were made deliberately and weren't just so that they could use all these fancy new libraries.
So I guess I'd liken it to Windows when it went from the 98 days to WinNT/2000 - keeping things working about the same while laying the foundation for bigger improvements later.
On the other hand, I don't see much downside to moving to neovim either. It is interchangeable (in my experience) with vanilla.
My vimrc is 80 lines, I don't feel it's vanilla at all, but I don't use :make or probably any other commands that launch subtasks so I guess this is what sets me apart.
I run linter every time I save, which made vim's UI lock for noticeable time on non trivially small files. With neovim linting is smooth as butter from UI/UX perspective. Also there is asynchronous make, and other possible features/plugins.