Nope.
it will be extremely hard without separating the modes both balance and design wise, which means they would get separate balance patches etc etc... Not sure Relic would commit that hard.
I disagree. The problems faced in 4v4/3v3 are often uniquely tied to that gamemode. Some examples:
1) JT/Elefant overperforming - many 4v4 have chokepoints and don't allow for actual flanking, there are also no indirect counters to these units (artillery which causes crits on them for example or an actual vulnerability for infantry attacks)
2) ForwardRetreatBase - this problem is almost exclusive to 3v3 and 4v4 and can also be handled as such
3) Ressource Inflation - How do you avoid ressource inflation? -> You don't give every team 3 damn safe territory points
4) Arty spam - again a problem of narrow maps (where you can't flank) and the lack/ineffectiveness(looking at you Panzerwerfer) of tools for counter-firing