It support plain and OpTeX (which I use often). bidi does not work with LuaTeX, and babel's implementation, while working with complex structures in LaTeX, fails in simple cases which annoys me: https://github.com/latex3/babel/issues/285, Ive tried to port Babel's code to different formats but it was harder as the code is somewhat convoluted between the Lua and TeX parts.
Babel already has three modes for LuaTeX, bidi=basic, bidi=default and bidi=basic-r, having another one wouldn't hurt ;)
I will probably use this package for polyglossia as well.