I would advocate for this. If your codebase is low in complexity then I think it would be wise to invest engineering time towards kotlin training. I've taken several courses on pluralsight and they get you up to speed quickly but informatively.

Also if you place kotlin in high regards or believe it saves you time/money as opposed to java (as i do too) then why not train java devs on kotlin and introduce them to a low complexity app before high complexity sets in (potentially)