I hope that having different classes means that they will be a lot more powerful at what they do. AV weaponry was pretty weak in PS1 and it took quite a few people to destroy a tank. Or, rather, to scare it away, as it usually had enough armor to run away.
Now, I'm hoping that, should I choose to play as an AV class, I will be able to destroy a tank with a couple of well-placed shots, much like in BFBC2. AV TTK should be a bit longer than in BFBC2, as vehicles will be more precious (assuming there's a long way to drive from a vehicle terminal-equipped facility to the objective). We definitely shouldn't be firing lock-on rubber AV missiles like in PS1, though.
By "a few well-placed shots" I'm thinking of being in a good position (hidden, with a good view of a tank's rear or sides) and firing 3-4 shots from a skill-based, dumb-fire or limited guidance launcher.
If I forgo heavy armor and powerful anti-personnel weaponry, I should be rewarded with some serious AV potential. It also makes me assume a role, not be one amongst a hundred identical players with MA/HA, AV, ReXO, Med and Engy.
Hordes of non-AV-class players should still be able to scare off a lone tank, looking for easy kills, with massed fire from whatever they have, though.