Multiturret tanks failed mainly due to targetting issues - it became almost impossible to aquire multiply targets for multiply turrets. Even 70 years ago small autocannons (which was main weapon for most tanks) didnt required that much place.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.
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Now, with modern FCS, glass/transparent cab, netcentric warfare, the multitargetting is possbile. That is why started to appear new multi-weapon vehiles like BMPT.