> you can bring over your vim config and it'll just work.

Except when it doesn't:

  $ nvim init.vim
  Error detected while processing /home/martin/.config/nvim/init.vim:
  line   44:
  E474: Invalid argument: completeopt=menuone,popuphidden,noselect
  line   50:
  E518: Unknown option: completepopup=highlight:Pmenu,border:off
  E824: Incompatible undo file: /home/martin/.cache/vim/undo/%home%martin%.config%nvim%init.vim

Or when opening a Go file:

  $ nvim a.go
  Error detected while processing function edc#init[34]..<SNR>66_apply[40]..<SNR>66_save:
  line    8:
  E121: Undefined variable: v:none
  E116: Invalid arguments for function get
  E15: Invalid expression: get(b:edc_save, a:setting, v:none) isnot v:none
  Error detected while processing function edc#init[34]..<SNR>66_apply[32]..<SNR>66_save:
  line    8:
  E121: Undefined variable: v:none
  E116: Invalid arguments for function get
  E15: Invalid expression: get(b:edc_save, a:setting, v:none) isnot v:none
  Error detected while processing function edc#init[34]..<SNR>66_apply[2]..<SNR>66_save:
  line    8:
  E121: Undefined variable: v:none
  E116: Invalid arguments for function get
  E15: Invalid expression: get(b:edc_save, a:setting, v:none) isnot v:none
  Error detected while processing function edc#init[34]..<SNR>66_apply[14]..<SNR>66_save:
  line    8:
  E121: Undefined variable: v:none
  E116: Invalid arguments for function get
  E15: Invalid expression: get(b:edc_save, a:setting, v:none) isnot v:none
  Error detected while processing function gopher#go#set_build_package[11]..gopher#go#module:
  line   12:
  E117: Unknown function: chdir

And they don't even always show properly on startup (just "press ENTER", need to use :messages).

There's loads of incompatibilities; some behaviour is different as well. I can't get it to stop clearing the terminal on exit for example; my 'nnoremap <Leader>p "*p' mapping just inserts '"', my Control+space mapping doesn't work for whatever reason, for some reason a lot of stuff looks different even though it has the same colour scheme, quite a number of my custom functions/commands/mappings error out for various reasons, etc. etc. And not all of these are very complex either: <C-Space> is a simple expression map: inoremap <expr> <C-@> pumvisible() ? "\<C-n>" : "\<C-x>\<C-u>" – Pressing <C-x><C-u> works, but this doesn't(?)

"You can bring over your vim config and it'll just work" might be true is you have a simple vimrc with a few basic ":set"s, but it breaks down very fast.