There's a script which seems to do what you want called
gen_Render selected item on new track, up to last VSTi.lua if you add this repo to ReaPack
https://raw.githubusercontent.com/EU...ster/index.xml
Also, not exactly what you're looking for, but I find myself often using the action:
SWS/AW: Render tracks to stereo stem tracks, obeying time selection