What's the deal with Neovim these days? Are people migrating or is Vim still the go to... Vim?

I switched to neovim about six years ago because completion backed by language servers was unusably-slow without neovim's asynchronous support. That was added to Vim in 8.0, and since then, there's been no difference between the two for my workflow. I use the same config for both Vim and neovim (save for a couple minor unimportant tweaks).

I don't think there's a compelling reason for many people to switch to neovim right now. I appreciate that the appearance of neovim was a real kick in the ass and prompted improvements in Vim. Vim had been essentially stagnant with no new features for a decade. It's now got frequent releases and tracks neovim's improvements closely. neovim's existence continues to improve Vim itself through innovation and competitive pressure.

I value neovim for how it's revitalized the Vim community, and I still use it mostly because while there's no reason for me to switch to neovim these days, there's also no reason to switch back.

As part of the neovim team and the author of the built in LSP for Neovim, I'd say that 0.5 is where things will really diverge. One of those factors is the built-in LSP support, but the others are the ramping up of Lua plugins being written, the extranges/extmarks features being worked on, the treesitter integration, and some other features I won't mention for fear of drumming up premature hype.

I completely agree with you otherwise. Neovim inspired Vim/Bram to kick things back into gear, and Neovim also took some inspiration from Vim's ideas, and the two have been close for a while, but the Lua integration is beginning to pay dividends which will cause a wider rift. Vimscript is not an ergonomic programming language or very performant compared to Lua, and I'm pretty sure that everyone can agree with that.

E: Oh, and I plan to make an answer to KillerSheep for the 0.5 release that will hopefully be equally or more impressive. :P

So, why aren’t you making these contributions directly to vim? Are the maintainers there not open to PRs?

Maintainer, not maintainers. If you look at the vim repo, https://github.com/vim/vim, essentially all commits are from the same person. Encouraging contributions and splitting maintenance between multiple people was one of the key factors when forking neovim. IIRC neovim was a result of Bram, the vim creator, refusing a PR for async plugins. Functionality that is today regarded as extremely important.