That would be horrible. There were so many things that made 2142 what it was. Walkers, Hover tanks, gunships, APCs, they were all inherently different from what BF2 had to offer.

The tanks in 2142 were high risk, but essential to the balance of the game. Tanks were threats at a distance, but weak up close. One shot in the ass they were dead, 2 shots in the side they are dead, the front took a lot of shit but that was the dynamic, keeping everything focused on that front. They could snipe walkers, and rape infantry all with just 1 high damage splash shot per few seconds.

Walkers allowed the IFV style of play, kill a lot of shit with little remorse, while still being very vunerable to specific areas and allowing for a major mobility increase(stepping over obstacles.). You could snipe infantry with 2 accurate shots of your main turrets, and still have enough left over to decimate groups of people from medium-long range. You also had a really unique mechwarrier-esque anti vehicle system with curving AT missle launchers that required you to land multiple shots to actually kill something. Not only to mention you had to protect your ass AND your crotch. The Battlewalker was THE Masculine weapon, in shape, form, and pain.

APC's EMP, machine gun, 2nd seat 3shot mortar, and mobile pod launch system is just iconic to the game. It is almost the same thing as the amtrac in BF3, only problem is the driver seat doesn't have any defense system, the mortar has 10shots and shit splash, and it is slow as fuck. These guys were tough, but also had vulnerable areas. Due to the fact that it isn't as capable at killing masses like the first 2 vehicles(Unless you had it in the hands of a good squad) its vunerable areas are again the sides and ass but in both of those areas it is 2 shot to bring it down to burning.

As of now BF3 is missing major teamplay elements that made Battlefield the true standard for teamplay in any game. VoIP allowed the Squad leaders to give good orders and allow the entire squad to communicate, commanders gave so much to the battlefield without having to rely on 6 people on your team to go mortar to give you a good fire support. The commander's ability to rely information from squad to squad and to see what others couldn't allowed battlefield to be what it was meant to be. > A tactical team based shooter. Without one person in a leadership position not doing their job the team would crumble and be raped by the other team playing team.

Just putting a titan into BF3 would not make it 2143 in anyway. You can already experience what a battle on a titan is like by playing metro, because metro is exactly the size of a titan. The reality of BF3 compared to 2142 is that if you ever played shuia taiba you know, YOU KNOW that even operation firestorm is small compared to that.

tl;dr no it wouldn't.