I agree that you would not want material standardization. But as long as you don't start combining mortar and howitzer units I don't think that would be much of a danger.

As long as mortar platoons stay at battalion and mortar sections stay at company the fact that you have different types of infantry units - mech, Stryker, parachute, air assault, etc. - should be all the safeguard needed against material standardization. I doubt you would see heavy mortars start appearing in a light rifle company's mortar section or howitzers in a light infantry battalion's mortar platoon.

I wasn't thinking that there should be a combined unit; just wondering if it would be benificial to have a single fire support MOS that would do a mortar tour for a few years, a howitzer tour for a few years, etc.

I don't know enough about fire support systems to know how difficult it would be to be proficienct in going back and forth from tube to gun every few years.