Would be nice if future commanders added a Pershing tank. I don't get why people wouldn't want it in for more variety and play style choices.
From experience, it would be abused into teching into tier 1 or 2 (or both) into Pershing. Performance of callins vastly beat that of stock units, so its better to ignore the tank tiers and skip straight into the callin. The Pershing, probably being one of the only tough USF tanks (i can only think of a possible only 3), will suffer the same fate.
Variety is but an excuse.