I think someone should make an all metal, very heavy SMG, of MAC size, with a quality side folding stock (or one like the MP5 has), ROF of 1200 RPM, accurate and reliable, closed bolt, with good sights and a couple off picatinny rails.
There are modifications out there that turn a MAC into that, for about 2000 dollars or so, plus the cost of the gun.
Personally I don't see a problem with the rate of fire. Use bursts at long range, and full auto when its best (room distance).
IMO if someone made a new gun like that (heavy, suppressor, full auto, high ROF and in 9mm and .45), and built with the quality of an MP5, I think SWAT teams and such would start using it. They've used MACs and American 180s before, I think they just stopped because those companies had a rocky time staying in business, and then the MP5 came along.