When the Makeyev Design Bureau announced that the May 20, 2011 launch was part of a Liner SLBM flight test program, my money was on this being a version of the R-29RM Sineva missile with more than four warheads. It appears that this is indeed the case - one report quotes a Makeyev press-release as saying that Liner can carry "1.5-2 times more warheads than Bulava" (I cannot find the original press-release, though). Since Bulava is believed to be carrying six warheads, this would make Liner carry anywhere from 9 to 12. Most likely the number is ten - this is the number of warheads the original R-29RM missile was tested with back in the 1980.
The warheads would be very small - probably similar to the ones developed for the R-39 missile, with weight of about 130 kg each and yield of 75 kt. But Soviet/Russian SLBM warheads most likely never had a mission that would call for high yield anyway, so I would doubt if anybody in Russia would be concerned about warhead yield - it's the number of warheads that seems to matter.
It is not surprising that Russia wants to increase the number of warheads on its ballistic missiles - as far as this number is concerned, Russia is already below the New START limit, so there is plenty of room for deployment. This is why we see the projects like RS-24 and now Liner. Not to mention the new MIRVed ICBM. I guess it would take Russia some time to realize that inflating the number of warheads does nothing for security, but at this point the urge to go for more warheads (and keep the proverbial strategic parity with the United States) seems to be too strong to resist.