As far as I can tell, this is the way to add larger SRVs. Unfortunately, since only 10 ships have a fighter bay this would prevent most ships from being able to use the larger SRVs. That said, half of the ships that wouldn't get the ability to use the larger SRVs would be small ships that would have no business deploying an SLF-sized vehicle in the first place.You're right about the dimensions being a big limiting factor, however a way around that would be to use the SLF bays for low altitude air dropping much larger ground vehicles.
While I am in favour of having larger SRVs deploy from the fighter bay, I think we should get more SRVs that can fit in the cargo hatch before we give larger ships even more capabilities that small ships don't have.