You have to ask, what was the problem needing to be solved that hasn't been fixed with better answers?
With the action in the stock, there's no way to adjust length of pull, and a folding stock will never happen. The mag well is obviously behind the grip, which adds difficulty to fast mag changes. You wind up pulling the stock off the shoulder, which loses the sight picture.
They were an answer to getting full power from carbine length guns, but the real issue is that combat soldiers don't need full power cartridges anyway. We've also advanced powders and cartridge designs a bit since the first kickoff in designs back in the sixties. Anyone using a 6.x alternative caliber in the AR would be more than happy to explain all about that with charts, graphs, and tables of bullet drop.
Point being, a sidefolding piston AR in an alternate caliber will do more and better, and many would argue using any standard design would do as well. Bullpups are just a collectible sideshow, and it's already noted one nation is seriously investigating a intermediate FAL replacement for theirs. The Brits just bought some American AR10 based guns for SWAsia, not bullpups, which they already had. Apparently they weren't accurate enough for the role.
If there is a clue, look which adopt them - mostly first world nations with extensive bureaucracies entangling their military. I don't know of one new design, other than China's, and none of the Improved Carbine test guns from FN, Colt, SIG, HK, Beretta, Remington, or whoever submitted one.
Bullpups don't fix anything that needed to be.