I've heard a few rumors of that, but the measure before the Assembly so far hasn't singled out particular classes of vehicle. I'm not sure that they'd get as much money as they want if they limited the scope that much. Plus the SUV drivers are the archetypal Soccer Moms. I was talking to one the other day, and she was livid about how much the state is taxing her family.
I doubt very much that the Democrats would try to pick on SUVs. The Car Tax is based on a fixed percentage of the value of the vehicle, so more expensive vehicles already pay a higher fee. The Democrats want to take advantage of the fact that the 1998 bill to reduce that percentage rate also allowed it to be restored up to the original rate if the State ran short of money.
The Dems believe they can restore the rate with a majority vote instead of a 2/3 supermajority vote (which is what tax increases normally require), and legally they may be right. At least they have a plausible case to argue in court. But if they start mucking around with the underlying law (i.e., singling out SUVs) instead of just restoring the rate, their case will fall apart. Then they'd need a 2/3 vote, and there are enough Republicans to block that.
Bottom line: SUV will not be targeted, and everyone will feel the pain.