Lets see if I can't take a real leap here, one bound to cause some controversy (yeah, here I go again, can't resist :unknown )
Multi-turreted tanks failed because of the increase in surface area resulted in thinnner armor or too much weight... or both, However, massive slabs of armor may become a thing of the past if active counter measures can be made as effective for vehicles as they have for warships.
If this happens, things will change as radically for tanks as they did for warships in 1940-1990. "Tanks" may become light enough for the long-imagined Hovertank to appear. They could have mini-turrets at each corner for counter-measures. Lighter cannon or quick-loading missle launchers can replace current heavy cannon. A second large turret with a semi-automatic mortar could give Tanks inderect fire capability for the first time.
I don't expect to see any of this in my lifetime, but the current generation of front-line tanks have been in service longer than any previous crop. It seems as if the true "tank" has been perfected, within economic limits. The next generation might be such bastardized oddities (such as the one above) that historians will deny that they are true Armored Fighting Vehicles. Perhaps the machines we are familiar with will be the last word in Panzers?