First of all, we all agree that buggies are awesome, right? Empire-specific ones, of course - the Harasser was a waste of space.
I know that buggies haven't yet been announced for PS2, but info about tank-mounted AA makes me worry that they won't be in.
After all, why design something that most likely won't be used?
A buggy would be statistically inferior to a tank in every meaningful way.
A tank will always have superior main weaponry, both against squishies and vehicles.
And even if a buggy had a proper, dedicated AA gun, like the flak cannon on the Skyguard, it would be more convenient to just roll out a tank with decent AA. Let's face it, a month after launch every single tank will roll out with secondary AA.
Also, if they looked to Battlefield for thoughts on how buggies work in modern games, they would determine that they suck balls and aren't worth implementing. Buggies in Battlefield are made out of paper, are barely armed, and can at best be used for lulz, stunts and as C4 buckets.
While they may not go to BF's extreme, vehicles in PS2 will likely be less durable than in PS1, so a "modern" buggy may end up being so fragile, that it's actually useless, unless it gets some special abilities like immunity to mines, so that it can use its strongest trait - mobility - to its full extent.
On a side note, just how awesome would it be to drive a Marauder (assuming it's still as rednecky as it was in PS1) with a flak cannon?