With only two doctrines with the MHT, I really wish there were more options to choose from.
I'm abstaining from this one. I certainly like the idea. Mortar HT upgrade would definitely have to be gated behind tech or CP somehow seeing as the 250 isn't restricted to a CP requirement (besides the one callin with the mechanized panzergrens).
It would certainly allow the 250 to be more useful in 4v4 matches, as the 250 very quickly becomes obsolete while the mortar halftrack is pretty useful for quite some time afterwards.