i think weve already had a chat on this topic- im not a fan of it for the reasons you listed. there are 2 commanders with the is-2 and if i pick one to use the is-2 and miss out because my team mate didnt build a single tank to squirt his out first.... it would lead to a lot of drops, grieving and generally shitty team mates. it would ruin the game i think.
imagine your buddy purposely NOT helping save your heavy because they want to build their own....
I know, that's the main concern, really. It would work fine in arranged teams, but it would catalyse even stupider decisions being made by random players.
Despite arguments that it would "Reduce build diversity", I'd like to see caps of some sort trialled. Generally people don't "Specialise" as has been suggested, what happens is that one side builds ten T-34/85s, and the other builds 10 PVs.
The thing with 3-4v4 is that concentration of force can too easily win you the game. Had a 3v3 yesterday, where despite bleeding my opposite counterpart hard, my teammates were having such an horrendous time that they allowed their counterparts to build up a KV1 and, like, four T-34/85s and suddenly barrel down the centre of the map and roll us into our base. In a 2v2 you might be able to deal with concentration of force like this, but one guy (And his two raketen) against all that? Not really happening. I probably should have had more mines around, but I was strapped for Munitions (and Sturm man-hours) due to hard fighting down the centre of Across the Rhein.
Even if factions have the tools to deal with these sorts of things (Which I'm not certain they do, not without heavy fuel investment, at least), a single person can't do much against such a large wave. Perhaps expecting a single person to be able to deal with two/three at once is a little silly, but you can't always rely on your teammates.
(I'd have peeled off to help my teammates, but the opposing flank players kept trying to flank and crush me. I did make a mistake in building an LEFH a bit too early, but I think the singular Jagdpanzer I'd have been able to get out wouldn't have been enough to help. Man i wish OKW had handheld AT. Sturms don't count, especially not before the Balans patch.)