I'm assuming the Dissipator configuration (with the CAR-length gas system under the HGs) came about as a solution to the function problems associated with cutting off a rifle at 16" without adjusting the gas port size. It's effectively a regular CAR gas system which we know works.
I think N3rday is suggesting that they make a "Dissipator" without the extra gas system--a 20" cut down to 16". Kurt and others have shown that this can work, if you adjust the gas port size. This would be better than the current Dissipator since it'll save a bit of weight by not having the extra gas block. (And associated thcker spot in the barrel).
What gvidon212 is asking for would have no weight gain over the current set up. It might have a slight reliability gain over the CAR gas system, but since nobody seems to think the CAR system is too unreliable I don't think it'd be worth the trouble.
I do think that if Bushmaster started making a regular mid-length like Armalite and RRA they'd sell a whole lot of them. Especially if they made them thin under the HGs and 1/7 twist. I know I would've bought that instead of the RRA I bought a year ago if it had been available. And since they appear to be using mid-length HGs on the .308 carbines they already have all the parts in stock.