I’d really like TextMate to support the Language Server Protocol for
code completion, navigation etc. for various languages (in my case
primarily Ruby, but LSP as such is language-agnostic).
To be honest, I don't have any clue (yet) what exactly needs to be
done. However, there’s a already a vast amount of editors supporting
LSP (see
https://langserver.org/#implementations-client ) and I’m
quite sure that investigating some of these implementations would
give hints about how to add LSP support to TextMate.