There are a few tanks that could be added that might see some use in the MA.
For Britain the Cromwell was roughly equivalent to the 75mm Sherman but was a fair bit faster.
The later Comet was better protected and had a similar gun to the Firefly, this would be the best of the British tanks.
The Churchill was well protected but had a similar gun to the 75mm Sherman and was too slow to see much use in the MA. However the special engineer AVRE versions might be useful if HTC introduced bunkers or obstacles like ditches to the game.
The Archer would make a good cheap tank destroyer as it had a 17 pdr gun. It was an odd design though with the gun mounted in the rear. The idea was it could set up an ambush, fire a few shots and then retreat quickly to a new position without having to turn round.
For the USA there is the Pershing heavy tank and the lightly armoured M36 tank destroyer, both armed with a 90mm gun.
For the Soviets the Su 100 tank destroyer would see a fair bit of use. HTC might even be able to add the Su-85 or Su-122 gun options onto the same shape like they did for the Panzer IV F1/F2.
Also there is the heavy tank chassis developments like the KV-1, KV-85 or IS-2.
Germany has a few competitive tank destroyers yet to be done, but they wouldn't really add anything to what is already in the game. The Italian and Japanese tanks would all be MA hangar queens.