I personally believe that the concept of the BMPT derives from the fact that a BMP type vehicle in a heavy brigade will be next to impossible to create as the internal volume is greatly reduced with the heavier armour, so putting BMP level firepower, while retaining MBT protection means that there is no space left for the Troops... and being a troop transport that would be bad.
My personal take initially was that the BMPT was an attempt to keep BMP firepower (ie 30mm cannon and 100mm rifled HE firepower in weapons capable of high elevation to hit targets tank guns can't elevate to hit) but in a vehicle with MBT level protection without the dangerous mixture of crew/troops and large amounts of ammo.
This would mean that in the heavy brigade, you would have a BTR-T heavy troop transport with maybe a single 30mm cannon and coaxial PKT, and instead of the BMPT carrying heavy gun armament and troops it would just carry heavy armament. This fire support type vehicle could help tanks operate more independently from infantry support, and also be a useful vehicle for convoy escort or in lower intensity operations in place of a MBT as it would be a gun platform with MBT level armour, but its weapons would be more versatile and useful than a tanks gun.
Then Medo pointed out that the Soviets and Russians often used anti aircraft gun vehicles in the direct fire ground support role... including the BTR-40 with twin 14.5mm HMGs which was designed from the start to engage both ground and air targets, on through the ZSU-57-2, ZSU-23-4, and Tunguska.
I think the Russians themselves are not totally sure what they want, but one of the 'stans (Kazahstan I think) has actually bought some BMPTs, so they do have some future. I personally think a change in weapons would be useful.
The new Armata chassis which the final BMPT will be based on will have three crew positions in the front hull, so I think a redesign of the turret to add more ammo below the turret ring and perhaps allow the replacement of the two single 30mm 2A42 cannon with a single GSh-30K twin barrel cannon that can fire either at 300 rounds per minute allowing single shots to be fired, or 2,000 rounds per minute to be fired when real firepower is needed, plus the addition of the 100mm gun from the BMP-3 which has very compact and efficient ammo choices including guided missiles would greatly add to the firepower of the vehicle. If you look back through this thread I have discussed this several times already... \
The idea of the brigades is chassis unification, so upgrading T-72s costs the least at the moment yet gives them a tank with the night vision and communications and data sharing capability of a new T-90 are far less cost. They probably have 10,000 T-72s, which means they will have a lot of chassis for the other vehicles in each heavy brigade. It would not make sense to just use the T-72 chassis for BMPTs as they are slightly different from T-90s and the soon to enter service Armatas. If you use T-72s and T-80s and T-90s... which they want to do initially it makes sense to make each heavy brigade homogenious... so a unit with T-80 MBTs should have T-80 chassis for all the other vehicles in that brigade so the logistics tail for that particular brigade needs T-80 components and tools and equipment.
There will be upgraded T-72 brigades, T-90 Brigades, T-80 brigades, and these will be replaced in time by Armata brigades when they are ready.
Being the top tank the Armata will likely enter service in the hot spots and danger areas first so Armata will likely start replacing T-90s and T-80s, but unless those vehicles are damaged or worn out then they will likely be sent to other units to replace older more obsolete vehicles.