The rapture change is a massive nerf to disc priest mana regen and results in a loss of hundreds of mp5. Currently, you get rapture returns from pretty much all your direct healing spells and shield/divine aegis. After 3.1, you'll only get a single rapture return every 12 seconds from a shield absorb. I don't raid 25mans, but I've seen people throw out the number 700 mp5 for rapture returns on live in a raid environment. With the new rapture, you're looking at 260 mp5 for a 25k mana pool if you get the return every 12 seconds. If you only get it every 15 seconds (weakened soul debuff uptime), that's 208 mp5.