Based on the Detonator of course, not the Flare Gun, though I prefer this name as “Detonator Jumper” is clunky and “Det Jumper” is unclear. This is almost certainly the most commonly-requested reincarnation of the orange-colored -100% damage concept, with the runner up probably being the Boston Jumper. (But seriously, why would you want to give up the best way to give your Medic Uber?) A lot of other people are understandably opposed to the idea, especially those who think the Jumpers we already have are useless enough.
But I think it could work, especially if Valve drops the training pretense and lets it keep every alternate use beyond dealing damage. Because the Detonator is actually the most versatile secondary in Pyro’s arsenal from the amount of functions it has, and I think one focused on mobility can still fill a useful role in the Pyro’s arsenal, even a role the Detonator itself can’t. Just consider:
1) If it could still light enemies on fire. But the afterburn doesn’t deal any damage. Victims would see the flame particles on the borders of their screen, but they won’t flinch and the character won’t scream about being on fire. This would still allow Pyro to spycheck, tag faraway targets for teammate’s benefit, and gain critical hits with the Axtinguisher and teammate’s flare guns.
2) If it could still destroy enemy stickies. Most people forget the Detonator can do this, but it’s one of my favorite features. Since stickies are one of the few projectiles not particularly well countered by the airblast, this function gives the Pyro some well-rounded coverage that he doesn’t deserve to lose just because his flares can’t deal damage.
3) If it could still carry the intel. I know Valve removed the ability for Jumper wielders to carry the briefcase because apparently they want nothing to do with the concept of flagrunning anymore, but this Flare Jumper is very much a secondary weapon. I’m positive that this treatment wouldn’t be needed; he’s still the same flamethrowing class as before, just with a bit more mobility.
And that’s it. Still an awful lot of features for a single weapon if you ask me. If you’re wondering how the user’s supposed to know all these secondary functions are still active even when the Flare Jumper doesn’t deal normal damage…I don’t know. Who cares, Valve’s always been sparse on the details for flare guns. The Flare Gun’s description doesn’t tell the user anything. And finally, if you don’t think the Detonator jump is good enough to be worth dedicating a weapon slot to, you need to check out the Pyro Mobility Repertoire or other sources dedicated to it. It’s an amazing ability that can really open up options for the skilled Pyro, and I would love to see this mobility option given more coverage in a dedicated jumper weapon.