I haven't read the comments Gazputin mentions from Rogozin, but comments about bigger missiles being more useful for satellite launches does make sense as they will all have limited operational life spans and it is important these days when making products to think about disposal after they become obsolete.
Certainly the SS-18 an SS-19 weapons were very popular and very reliable satellite launch platforms, and I suspect Samartan will be very good too with it extra range potential.
I can see that the new START agreement was extended just in time, but it is unlikely that anything will replace it for the foreseeable future with HATO encroaching on Russian borders the US will likely demand Chinese nuclear weapons be included together with Russian totals and for tactical nukes to be included and I don't think Russia will agree to either unless the UK and French and even Israeli nukes get included too, not to mention all the complication of Russias new weapons like Thunderbird and Poseidon which they will demand are counted as strategic nukes too no doubt.
The biggest expense with ICBMs is their bases... either building silos or storage areas where they will be located... but most are already built.
The START 2 treaty banned heavy ICBMs so single warhead weapons only were allowed but the new START and its current extension lifted the ban on heavy ICBMs so some money could be saved building big heavy ICBMs to reduce the number of missiles needed to deliver the warheads, but improvements in technology should mean train based missiles could be a future possibility with scramjet powered cruise missiles becoming a potential new area.
Before ICBMs were possible both sides experimented with winged super long range cruise missiles... most had ranges of a few thousand kilometres and speeds of about mach 3 with ramjet propulsion... but the introduction of the R-7 and later ICBMs all work in that direction stopped because even a mach 3 aircraft could be shot down while a mach 10 plus IRBM or ICBM was relatively safe short of nuclear ABM systems.
Well scramjets mean the upper speed limit of platforms is no longer limited to mach 5-6, and much higher speeds are possible and weight is massively reduced if you just carry the fuel and scoop the air needed to burn the fuel from the atmosphere as you fly through the air.
3/4ths of rocket fuel by weight is oxidiser to burn the fuel... it will work in space and low oxygen environments but it basically quadruples the weight which means much more powerful rocket motors are needed which burns fuel at a higher rate meaning more fuel is needed in a vicious circle.
In comparison a scramjet motor is lighter than a rocket motor and burns fuel more efficiently and not only that it can be throttled precisely to optimise the fuel burn... a liquid fuelled rocket can do that too of course but not a solid rocket.
Only needing to carry the fuel makes the weapon much smaller and much lighter and also cheaper too.... meaning a missile that barely fits on an enormous custom designed truck could now fit on a rail wagon rather easily... and the mobility of a train is much better than a truck.