Well of course what they are waiting for is not aircraft to be built but engines to be ready... they could have restarted the Il-106 programme in 2005 when they started making money and things were better, but to be honest I suspect they didn't really have much need to fly things around... and most airfields were not in a great state either.
Air travel is fast, but rail or shipping is cheaper if it is an option and it continues to be cheaper if you support it properly.
With the arctic ports being revitalised and more people moving there... either directly with military bases, or just people looking for work, then expanding ports and adding rail lines from the ports heading down inland to settlements makes sense, because products and material extracted from the ground there would move far more efficiently by rail than by air... and transporting heavy items by rail and then by sea is much easier and much more efficient by rail.
A single rail car can carry hundreds of tons of weight... more than an entire aircraft, and you can fit hundreds of rail cars together with perhaps two or three engines to drag them north to a port so the contents can be put on a ship and sailed anywhere in the world.
Right now they have a window of time to think and plan, and so they will be looking at their own figures regarding what they have been carrying and how far and they will have a much better idea than we do about what they might need.
The An-124 is a good example... it can carry 120 tons a distance of just under 6,000km, but what if they need to take something 10,000km distance?
What if it is big and bulky but not really actually heavy... the An-124 could carry a 40 ton object 12,000km... more often than not loads are not carried by the An-124 because they are very heavy, but because they are big and don't fit inside other aircraft and have to be broken down into pieces and carried separately.
If they are talking about making the Il-106 physically bigger, they are clearly interested in bulkier objects... the reduced fuel 120 ton capacity will likely be a military emergency thing and what they will probably do is refuel the aircraft in flight to restore some of the lost range because of offloaded fuel for takeoff.
Even made bigger the Il-106 should be cheaper to operate than the An-124 with the bigger engines and so it makes sense to build them as soon as is reasonably possible (which as I said is pointless until the engines are ready).
The irony is that the urgency was originally to replace the An-22, but the An-124 managed the job well enough, but now they want all the Antonovs gone from service that might not actually happen very quickly because the An-124 is made in Russia, it is only the engines that are Ukrainian so the new engines that make the Il-106 possible, will also be suitable to eliminate the Ukrainian engines from the An-124 as well.
Of course they are about to introduce a range of new types of armoured vehicle, and of course IRBM and IRCM carrying trucks that could do with being flown 12,000km and launched, so they might expand their needs for heavy aircraft... but as I keep saying most of the time for postal services you don't want to wait until a huge aircraft is full before you deliver it because it might take days or weeks to fill it up properly... which means most of the time it will be operating with a light load.
If you currently use 3-4 Il-76s a day then you could probably replace them with one An-124, but the problem is that some days you might only use one Il-76 in which case your An-124 will not be very efficient... but then keeping 2-3 other Il-76s on standby is not hugely efficient either... you wont know until it is too late that you wont be needing them... except around certain events when traffic peaks.
or use lower power settings to save fuel.
Sounds OK in theory, but think in terms of a car... put a V8 into a car and you find you will burn a lot more fuel. It might actually help a lot if you tow a caravan or boat, but in this case the smaller aircraft is getting the engine power of a much larger and much heavier aircraft... it normally doesn't work.
Maybe go for PD-18s instead of PD-24s?