With some simple rules on what is expected for 3.x module formats, function reference, db access etc the original module developers could re-write their creations for you. I'd be happy to do it for the few i've contributed.
You could also state what community modules you would like to include in a base 3.x bot and ask the contributer if they want to update it, if not ask the community if anyone would like the task of updating a specific module.