I'm in the process of doing this switch on a MTB. Main reason is that the existing suspension fork is frozen up and the reasonably priced replacement fork I found for it is a threadless. The bonus is that I already had a stem that will fit the new fork and a spare set of MTB handlebars I also had on hand. So, all I really needed to buy was a threadless headseat of the proper size. Found a FSA Hammer headset for $13 so with that and the new fork, I should pretty much be in business.

Only other issue is that the original fork had cantilever brakes and it had a cable stop integrated into the fork whereas the new one does not but it does have a mounting hole where I can rig one up. The other option would be to mount a V-brake on the front which isn't that great of an option because it would differ from the rear brake. I'm pretty sure I can fabricate a cable stop with some scrap steel I have on hand and a bit of welding.