Yea, interestingly enough, most complaints about bullpups are ergonomics, rather than anything technical. Bolt, Barrel, Receiver, Trigger -- BANG.
But, save for the actual weight, it's hard to imagine a need for a BMG bull pup.
As was said, the triggers simply suck, and the trigger is a primary component for long range accuracy.
You don't shoot these things off hand, heck you don't shoot these things anywhere save on a rest.
If you want compactness for travel, a folding stock would make more sense than a bull pup. Doesn't affect weight, tho.
Another complaint about bull pups in general is that they have a much shorter sighting distance with the shorter barrel. This is mitigated by optical sights, particularly today, but in the past this was a factor.
Bull pups are "cool", but everything interesting on them are simply in the wrong places.