Active Flow is a buff you get for playing offensively, opposite to Negative Penalty in Xrd. You deal more damage, recover more burst, and more. It activates when you continually go on the offensive.
Exceed Accel is basically a new Distortion Finish that you activate when you're in Overdrive. If you hit a specific move in a string, you will end in Exceed Accel and do a ton of damage in exchange for ending your Overdrive.
Xrd will add more to it's depth in the later revisions and it will be faster, I hope more faster rather than less so. It won't be as difficult or as technical as AC+R but it can definitely be faster paced and more technical as we saw with Blazblue's additions.