Jabari is not a fashion designer actually. Don't get me wrong he loves fashion but after the events of Team Flare and how Diantha didn't bother to leave her movie set to help out Jabari puts most of his time while Kalos champion into actually being the champion (i.e. patrolling the region and trying to keep threats at bay). After he's dethroned he works closely with environmentalists and fashion designers to make more durable, eco-friendly gear for trainers and athletes.

If Jabari had not become champion (and he would've decided not to take on the league had Diantha and the other Elite 4 had actually done their jobs, he pretty much only took on the league to figure out what was up) He definitely would have pursuing fashion design as a career using Serena, his boyfriend Grant and his cousin Cami as models mainly focusing on active wear but also doing high fashion as well