As 99% of the people here appear to be incapable of answering the question at hand I will.
I dont know if there are any plans for a BF3, but as EA is a company they will understand that they have hit a gold mine. For that reason I think its pretty clear that they will at some point be bringing out another version. I would assume it will be announced within the next year or so.
I would like to see a revamp of BF2. Ive only played that, SF, and 2142. I find BF2/SF to be more fun.
New maps
4 Armies (the current 3 + a new one: eg the EU. The problem with that expansion was it was 1 new army Vs then old ones.. and as everyone wanted their Euro Force Medal most servers had stacked teams. I doubt they will ever introduce an exp pack with 1 army in again I bet that much.)
Nice new guns, but also some of the old ones.
A new graphics engine. Something a little more eye friendly would be nice. The same sort of physics in terms of the way the people move.. you should be able to see your feet/ your hands when going up a ladder.
Players should be able to choose when and when not to have their combat goggles on. Like if there is lots of dust in the air because of a helo landing players with their goggles of would have impaired vision.
Weather systems of levels: the wind will blow up some dust now and then. On some maps perhaps there is snow falling/ on the ground.. so the movement of vehicles is changed slightly. Rain also...
When the vehicles are damaged their handling changes: A jet which is damaged will be less responsive.
When vehicles are destroyed the animation and physics of the explosion should be better. Floating aircraft shell is a little lame:)
Last idea is a little weird.. but could be cool. When it comes to supply drops, it is dropped form a transport aircraft. Like a C130:
http://home.cfl.rr.com/aircraftmodels/images/c130-1.jpgThis is piloted by 2 crew members. The pilot does the flying and the second is in charge of when to drop the supply's. They would have to work together to drop them at the right location on time. They would be in direct contact with the commander. They would get teams points for doing this.. but the catch is they have to re land to resupply. So skill would play a part of being successful.
Those are my ideas on what would be good.. no idea what would happen.. but Im sure they will bring out something within 2 years.
Please excuse any grammar.