They could do new advanced jobs eg. Lv 50 whm + Lv 50 bkm unlocks a quest line for the red mage soul stone. As a red mage you can use staves which unlock all whm skills or tomes which unlock all bkm skills or rapier which unlock a preset whm and bkm skills.

Same could be done for samurai or dark knight or any of the other popular classes.

Just an idea on how to get new jobs to work with the current system