I think the main problem with carrying lots of warheads would be space in the warhead bus. They would probably need a nose extension and perhaps multiple bus’s to carry 20-30 warheads.

It would certainly save a lot of money having 1,500 warheads in 50 missiles than having 1,500 warheads in 150 missiles… fewer ICBM bases, fewer actual missiles etc etc.

Regarding the “Hypersonic Glide Vehicle. Tested from STILLETO earlier this year” …forgive my ignorance but I would have thought all reentry vehicles would be hypersonic from ICBMs, and the US supposedly introduced MARVs a long time ago, so I don’t think a manouvering reentry vehicle is new. I think the new weapon might have MARV warheads for improved accuracy, but the new technology that no other nuclear power has is probably either plasma stealth for the warheads or mobile missile launchers (rail or vehicle based). I tend to prefer the former, but it could be either or both.