Right now Russia is developing a new tank and highly likely mobility is the corner stone of new doctrine it will be in 40 T class [ 40 - 49 T ] much like T-90's.
Indeed that would fit their needs, there was a lot of talk in the west about tanks made out of various types of plastics that were light and easy to fix and the plastic acted as an effective armour.
Perhaps automating the tank further to a 2 man crew might enable a tank be further reduced in size too.
So heavy armour with powerful engine will mean better protection and mobility.
Or better armour. Currently western armour is bulky and heavy, while the Soviets/Russians have gone for all sorts of different types of protection including ERA to reduce armour weight and vehicle size.
So how does one justify having a 48T Tank like T-90 over say a 70T tank like Abrams.
At the end of the day no tank is invincible and so it is a case of determining what the threats are and what can be done to protect your tank from them while still keeping it mobile and with a weapon that makes the whole vehicle useful.
From a design point of view there are things you need and things you don't need. For example most western tanks have a human loader. The extra internal volume for one extra man plus their kit and that extra space in the turret. This has to be protected so you increase the size of the armour to protect the extra internal volume.
In Russian vehicles the loader has been replaced by an auto loading mechanism. This reduces the size of the turret which means it needs less armour to protect the crew. Remember the armour on the front of the turret is the most likely hit in combat so it is also the thickest and heaviest armour on the tank. The smaller you can make the front of the turret the better.
Also rather than having extra layers of armour on the exterior of the tank the Russians also use ERA of various types to increase the effectiveness of the existing armour plate.
This is a bit like angling armour so with a minor increase in weight the armour protection provided is greatly improved.
I would also add that the US has a program to design and build a 40 ton class tank... it has been shown on their future weapons programs on discovery channel. It looks like an Abrams that has been in a car crusher and crushed down by 1/3rd. The barrel is square on an angle so it looks like a diamond shape end on.
We are going to have to import some technologies to build true modern tanks.
I disagree. I think an upgraded T-90 will be fine for the next decade. In fact I believe it has been mentioned that when the T-95 program lost funding that they said they would concentrate on upgrades of the T-90. With new Armour and new FCS and new EO jammer and new ERA that covers it better, with modern French ESSM and Catherine Thermal imagers, with new communcations and battle management systems, with a new turret bustle autoloader that allows the tank to operate with no free ammo in the crew compartment and allowing longer penetrators to be used I think it will be an excellent front line tank for a decade or more.
I would think the weight and logistics would have played its part in cancelling besides using a 152 mm Smooth Bore which is clearly not the standard with existing gun of 125 mm type.
I would think when they get rid of the older tanks one advantage they will enjoy is that they will have standardised their tank fleet to 125mm calibre high velocity guns.
A 152mm smoothbore will make fire and forget tube launched missiles a serious option because of the calibre with the added bonus of offering diving top attack threats to Russias enemies and the larger calibre HEAT warhead will be much more effective because of its extra calibre alone.
I would think that the next gen tank will have a lot of the new technologies that were developed for the T-95. The difference will be that when it appears the new T-95 will be like the Su-35S... a totally new design in the sense that most of the internals are Russian, but also much better than the old aircraft in performance in every way.
I would expect that 152mm calibre would allow a gun tube launched UAV with fold out wings that can be launched ahead of an armoured unit and the imagery could be watched by all the vehicles in the unit with one vehicle commanding the UAV to find targets or check for damage... it could even be fitted with a warhead if it finds a soft target.
To create a next gen tank you will need a next gen army for it to operate within, so C4IR needs to be much further developed before a new tank will likely be needed.
Personally I am more interested in the medium brigades, because with BMP levels of armour and mobility it will make the further development of the BMP-3 with the UAE very interesting. Will they retain the layout and preserve amphibious capability, or will they go for the 30-35 ton Bradley approach and give up gun ports and amphibious capability.