Drastic decrease in MP usage for one, done in large by Dark Arts effects being added to base effects which is basically saying we no longer spend MP to gain them. Also the Sole Survivor concept basically refunds the MP cost if you use Dark Arts as well as grant an added effect. I'm all for buffing Sole Survivor to make it more useful during a battle but that's over the top.
I mean I'm all for a buff to DRK so it is more on par with PLD and WAR but some of the idea collections I am seeing posted in this thread will make DRK considerably OP and as a result will never happen. Some ideas aren't too over the top but still...