I still have my reservations about the sheer number of types of APCs and IFVs you believe may be fielded after 2015. Even the USSR did not have that many types. IMHO, there might be some consolidation somewhere just because of finances.
I agree the process will not be instant, but the theory is that each brigade has one chassis type so that all its vehicles share the same mobility and same parts, and similar levels of protection.
Each Heavy brigade for example will need a lot of Armata chassis, and I think their plan for 2000 operational tanks and 4-5000 tanks in reserve will result in a force... initially of T-80s and T-90s and late model T-72s as the 2,000 operational tanks with the 4-5,000 reserve tanks mostly being upgraded T-72s. This means most of the other vehicles in support of those vehicles could be T-90 or T-72 based like the MSTA, the BTR-T, the BREM, etc etc.
As Armata enters production they will make tanks, BMPs, artillery, air defence vehicles, armoured recovery vehicles etc etc based on the Armata chassis and when a complete brigade of vehicles is ready it will replace an old unit whose tanks can be scrapped if worn out or sent to the reserve and the oldest and most worn out vehicles there can be withdrawn or donated/sold.
In the medium brigades they can use BMP-3s and BMP-2s and BMP-1s and BTR-80s and BTR-82s, but it is faster to produce lighter vehicles so I can see the light and medium brigades being upgraded faster. The BMPs will be replaced with the 25 ton Kurganets-25 and the BTRs will be replaced with the Kangaroo or Boomerang or whatever the wheeled replacement is called.
The light brigades will have BRDMs and BTR-82s and similar vehicles but will be replaced by one chassis called Typhoon.
The medium brigade "tank" would be the Sprut, but I rather suspect that they will only use Sprut for airborne forces for now and wait for the Kurganets-25, which will have better armour and optics and systems and a "tank" version will have a 125mm gun and a "tank" electronics suite. Hard to say whether they will make one or two versions as the Kangaroo or Boomerang might have a heavy gunned version too. If they adopt a 57/45mm gun for the new BMPs at all three levels it is possible the wheeled medium brigade "tank" vehicle and the wheeled light "tank" vehicle might have that weapon instead of a full power 125mm gun.
Speed will be important for these lighter vehicles but fire power will be important too.
Your arguments for the 57mm are convincing. How do you think an appropriate anti-tank round will perform against 21st century tanks? I doubt it will be able penetrate from the frontal arc. What do you think about shooting on the sides/rear? or should they rely solely on an outside mounted ATGM?
Technically they have always relied on missiles for anti tank performance, with the 73mm gun of the BMP-1 an emergency choice because of the close range gap in the AT-3 Saggers engagement envelope. Once the AT-4/-5 launcher had been retrofitted to the BMP-1 that gap was closed and the 73mm gun was simply used for its HE power... which wasn't totally amazing as its ammo was based on ammo for the SPG-9 recoilless rifle... externally it looked very similar to an RPG-7 rocket.
The 100mm rifled gun of the BMP-3 is significantly more effective and powerful, but even when firing guided missiles its effect on frontal armour of MBTs is marginal.
Of course the anti tank capacity of the BMP series is largely for self defence... BMP commanders should never go looking for enemy tanks.
I think Russians are realists and that they know they will not be able to airlift more than existing 4 VDV divisions and that other units will have to move around on roads and railroads. I'm sure this is one of the reasons, why Russia intensively build modern autoroads between European part of country and Far East and actually double trans-siberian railroad with BAM and other lines. Tracked vehicles will strategically move inside Russia by railroad, wheeled vehicles will drive on roads.
Personally I would like to see the VDV get their own aircraft as their deployment requirements mean they need to be able to be dropped pretty much anywhere, including the middle of no where.
For moving forces between military districts then air transport makes sense, and moves to put the An-124 back into production and to produce Il-476s, AND to buy An-70s suggests to me that they want to be able to move brigades between military districts by air.
As you point out however improvements in roads and rail infrastructure is also very important as it offers options and within military districts certainly heavy brigades will be better moved on rail than air, but light and medium forces will obviously have the best mobility.
One would assume that each military district will have allocated the forces needed to deal with any problems that might come up in their region, but there will be some situations where more force are needed. In those extreme cases forces from outside that district will need to be moved in, and likely moved in quickly. Each district will have its own VDV forces most likely, and being elite and quick to move other VDV forces from other districts might be moved in to support them, but the whole point of the restructure is to get rid of the low readiness units that would take a month or more to mobilise and be equipped with all high readiness forces that are able to react at short notice and to move to where they are needed quickly.
For 90% of issues the 4 military districts will have enough resources and men to deal with the problem. The ability to move resources around for that other 10% of the time and for mobility within the district means the forces will need mobility and speed... both strategic and theatre... mostly for medium and light brigades of course.