I am not familiar with TMCC. I wonder if it's possible to design a loco that all function wires terminate in a socket, into which either TMCC or PS3 could be plugged. The TMCC or PS3 need not utilize every terminal on the socket. This could save Atlas considerable money on inventory. Buy an ATlas loco, and have the dealer plug in a PS3, TMCC, or conventional reversing unit.
Unlikely. The only common item is LED lighting. Couplers, speaker impedance, and motor tach are different.