In an interview with CEO of MIC it is mentioned that the aim is to have 70 % commonality between Kurganets & Boomerang and modularity which should be good for long term logistics
The Kurganets and 25 ton class boomerang are going to be similar weights, so it makes sense to give them similar engine packs.
Armament and electronics/sensors will likely be the same too. Other than that screens and seats and controls can be standardised, with the seats designed to reduce the damage under floor mines do to the crew and passengers.
What is the commonality achieved between current BMP-3 and BTR-80/82 APC ?
Different weight classes and roles... one is an IFV and the other is an APC.
With Kurgan and Boomerang both are IFVs and APCs and tanks and everything else... and they are in the same weight class (ie medium) so it makes sense to have common engine and transmission... different running gear of course because they are tracked and wheeled, but in terms of weapon systems and electronics and sensors they can use the same stuff.
Good for logistics and training and purchasing economics.
Also it was mentioned that Kurganets will end up having 45/57 mm Gun which when compared to BMP-3 100 mm Gun is a downgrade but then I think the requirenments are not similar they are aiming for guided rounds in anti-aircraft role , so achieving a standardisation might be a priority over firepower.
The primary role of the main gun on the BMP-3 is to penetrate enemy IFVs... the 30mm gun no longer cuts it, and using 100mm guided missiles is expensive and they are for emergency use against tanks anyway... they only have 8.
With a 45/57mm gun they should manage a decent HE charge that is rather more than any 30mm cannon, though it wont be as powerful as a 100mm rifled gun. The armour piercing round for the 45/57mm gun will be able to defeat any non tank IFV from any angle out to 2,000m and with guided shells could perhaps even deal with helicopters and air targets out to as far as they can see them... 6-8km.
In other words not as good at HE as the 100mm, but still a useful HE shell, plus much better penetration and anti air capability than the 30mm gun.
That is not a bad compromise... especially when you keep in mind that several vehicles in the Brigade will have 120mm gun mortars with an even more powerful HE shell than the 100mm rifled weapons on the BMP-3, and heavy guided missiles as well.
The standard pattern was BMP-1 with 73mm gun and BTR-60s with 14.5mm HMG.
Then they introduced the BMP-2 with a 30mm cannon, but it did not replace the BMP-1 because they found the extra HE power of the 73mm gun complimented the 30mm cannon rather than the cannon replacing the 73mm weapon, so they used the 73mm gun with the 30mm cannon and 14.5mm HMG.
With the BMP-3 they replaced the 73mm gun with a 100mm rifled gun and kept the 30mm cannon with new ammo, and they added the BTR-80A with a 30mm cannon and the BTR-80 with the 14.5mm HMG.
I rather suspect that we will see in the new brigades vehicles with 45/57mm guns in the IFV role, but we will also see basic troop carriers (ie APCs or BTRs) with a 30mm cannon or a 14.5mm HMG.
I also suspect to make up for the direct fire HE that is lost with the BMP-3 they will compensate with 120mm rifled gun armed BMPT type vehicles, which together with 120mm Vena type vehicles (similar to the BMPT but without the extra gatling guns and grenade launchers... perhaps with one rifle calibre RWS and more 120mm ammo) which operates as a support vehicle for the unit.
The main difference between the two vehicles apart from the extra armament on the BMPT, is that the Vena type vehicle will mostly fire indirectly at targets it can't see directly, whereas the BMPT will be used as an anti ambush weapon for convoys and tank units... taking on Javelin launch teams and RPG teams whereever they hide... in trees, up cliffs, in tall buildings, etc.
This way they get both standardisation AND firepower.