I like the x64 decompiler a lot. Would it be possible to make just the decompiler as a plugin for x64dbg?

Its definitely possible, but I should make more improvements first. The decompiler plugin just needs memory to work with and returns JSON. Optionally, it can take parameters from the UI decompiler window, such as variable names and types, comments, function prototypes, etc., to make the decompilation more interactive and accurate