As it stands the M-8 can go after lightly armored targets; M-16s, M-3s, LVTs, and  other M-8s.  It can damage Panzers, and Shermans, with difficulty, and a well placed shot will kill them.  However it can not damage Tigers and T-34s.  That little 37mm popgun can not penetrate the thick armor of the Tiger, or  is deflected by the sloping armor of the T-34.  IMHO the M-8 trades firepower for speed,  wich makes it a balanced ride.  
Look at how the vehicles are balanced speed/firepower wise.  You will see that the fast movers are the most lightly armed.  Hitech has ballanced vehicles to the point where you have to choose: Do I want to get there quick, or do I want to kill everything that gets in my sights.
If you introduce something like the M-18 that has speed and enough firepower to take on the "BIG" boys, you will fundamentally change the game ballance.  I don't think Hitech will go for that.