I experimented with a fretted fiddle a few years ago and it worked to a certain extent. Your pitch up the neck is always spot on , but you can't get the slurs and slides, and that makes it less fun. I abandoned the idea after about a year. I've played a frettless guitar and it's fun. Someone reasonably prominent plays one but I've forgotten who it is. The banjo player with fiddler Ralph Blizzard (Rounder Records) plays all over the neck beautifully on a fretless instrument.