The pull ratio doesn't really matter, but, the total cable travel required does. If you go to a MTB rd, you may not be able to pull enough cable to get to all the cogs. I don't know any specifics, but I think it's something you'll need to consider.
These are designed to address that issue:
https://velo-orange.com/collections/...1s-dt-shifters
Sounds like a fun project, keep us posted on how it goes!
Chris