Oberon, the heaviest MIRVed ICBMs were always liquid fuelled ones.
All things considered they may be interested in ICBMs with storable liquid fuels due to how those are most efficient in terms of throw weight. For example Russia, despite mastering solid fuel MIRVed ICBMs (such as Yars) is still desighning a new generation liqiud fuel ICBM - Sarmat.
BMD stuff is not a significant issue in my opinion, as the BMD sites are well known and are covered by two EW systems, the EW radars and the new EW sats. While the sat force did suffer attrition, with the gap in capability occuring (2014?) it is now back to minimal capability (with more launches to go) and coverage of two nodes - Pacific and Atlantic from HEOs.
Specifically we have deployed new radar stations on Eastern direction, to improve EW in that direction:
You can read more here:
http://www.russianspaceweb.com/eks-network.html
http://russianforces.org/sprn/