I've always wondered and hoped that we will be able to equip abilities that we learned from other jobs with AP and that maybe we gain more AP by completing missions in the story line.
Also an alternative idea would be that maybe we could buy abilities and stats and equip them with AP and upgrade them every 5 levels or so. Example: You buy the ability 'fire' and the stat 'critical up' and it cost 10AP for fire and 5AP for critical up. You can upgrade and equip the same ability and stat again costing more AP, so if your lv50 you can equip any ability or stat up to 10 times increasing there effectiveness. This way you just pick and choose what abilities and stats you want and how powerful you want them to be.
Another example: You purchase 'HP Up' which cost 10AP to equip and gives you +100HP, each time you equip it it cost 10 more AP and gives +100 more HP. Any way just an idea tell me what you think.