Don't really think this should be a thing.
You can get up to 450 AP per rebirth, not including aging, per rebirth. While yes, this is considerably more limited than red coins, I imagine that, if this *were* added, it'd be just as punishing as the AP price, if not more. I'm pretty sure this was added just so that old players had something to throw AP at.
Interesting stat to claim considering you have an average level of 50 per rebirth