I’m interested as well. I’m using switch chip in ac² quite actively (vlans for loopback for in-line packet processing by IPS and jumbo 9k support. A bit similar to this http://forum.mikrotik.com/t/loopback-nat-is-performed-only-once/121914/1 just instead of second router IPS appliance. Lack of switch chip is deal breaker in L2 loopback scenario).
I never experienced thermal issues tbh. But you could always try downclocking a bit. hAP ac allows that (unlike CRS3xx switches for example duh)