Somehow many conversations keep going into tank design forgetting that tanks are just a part of the whole, and a much bigger whole in the case of Russian Army. The strategic outlook also has changed, and there is no longer an imperative to field tens of thousands of tanks against NATO.
There is a higher priority for lighter, more mobile and more fuel-efficient forces, so tank development will probably focus on upgrading existing fleet while the overall procurement will focus on forces protection, mobility and rapid deployment, which is a trend in other developed countries. This trend is more qualitative in nature then quantitative, and the emphasis is on personnel and training rather then on technology and systems.
Having said that, what more can be done for tank design?!
Tank design is governed by the ability of the crew to see targets. No one has suggested transforming the terrain over which tanks will be expected to fight because that would require either nuclear weapons, or prior agreement with the opponent ;-)
Given average engagement distances, either a 125 or a 120mm gun, and even advanced 105mm munitions will do the job most of the time (given a good crew). Making tanks heavier with armour would either slow them down further, or give even more accountants form various DoDs heart attacks over the fuel bills
Solution seems to me to be not larger guns, or more armour, but different ways of targeting, and using a greater mix of direct and indirect guided ammunition in tanks that would allow indirect engagement beyond the average LOS ranges. That was the thinking since the 1960s with T-64 and M60A2. Soviet designers may have been more successful with the idea, but the proliferation of lighter ATGWs in NATO countries may have been an alternative tactical direction. In any case the Israelis seem to be fast catching up with tank gun-fired missile technology, which is still not mature due to seeker-guidance limitations (related to materials tolerances in the electronic parts).
Considering that WW2 tank guns were a culmination of four generations of breach-loading development, I'm not surprised that two generations of gun-launched missile technology is not enough.
Cheers