> The code base is actually small and mostly written in Lua, so that it is actually possible to change the editor to your liking.

When I say extensibility, that's not what I mean. Code is available and it's small and mostly written in Lua - that's all good. But I don't want to mess with core because then syncing upstream is a huge pain. The only interface I want to deal with the extension interface. I haven't looked at the api yet, but I am skeptic about the claims. Vim has vimscript, Emacs has elisp, sublime has python...Editors has been providing extension interface for a long time.