I don't have an issue with having freelook inside of our cockpits. So long as weapons can only fire to the centerline of the torso (as they currently do when you are locked into first person view) then this works. The problem is that CryEngine2 doesn't have a clue what to do with freelook and it will make weapons fire in the direction of view, regardless of the surrounding geometry of the vehicle. If I'm standing with my torso centered to my feet and enter 3rd person to look over my right shoulder, if I fire weapons in this mode the bullets/lasers/etc will be shot out to my right, inconsistent with the geometry of the 'Mech (or any remote relation to reality). This is a BIG hurdle to overcome code-side and we have a ton of other features begging for attention first.
In addition to the above technical hurdle, having freelook in some of the 'Mech cockpits would be more than a tad anti-climatic. Think about having freelook inside a Novacat or an Awesome. There isn't a lot of "window" to begin with so you would be constrained to looking at the interior of the cockpit. Despite claims of "want to see how cool the cockpit looks" I think the novelty will wear off pretty quickly, especially for any vehicles that have non-protruding cockpits. This makes me (personally) question if the effort required will be justified by the outcome.
There is also the question of how freelook will be handled for non-'Mech vehicles. For aeros, this could be implemented as a really useful "turning your head" mechanic to see to the sides and above. For tanks, this gets a little weird because we have camera positions chosen based on optimal gameplay, not head-realistic driver position. Some would say "put the the camera where the commander/gunner/driver is" but I think the existing position makes the best compromise for having 1 player in a vehicle. Freelook might give a "side mirror" toggled view, and maybe even a quasi-top-down type view to allow for terrain navigation.
Regardless of how free look works, it should be a mode that, when toggled, disables your ability to fire weapons. There should be a transition interval (0.5 sec) when switching.
To the last point, I would not mind having some preset cameras that relayed set external views to the cockpit of a 'Mech. A "leg-centered ground cam" would be useful, as would a "reverse" cam looking straight out of the back of the 'Mech. In my opinion, these views would be toggled through on a sub-monitor. With the addition of a sub-monitor, we could introduce things like gun-camera, remote camera drones, shared camera for commander view, etc.
As far as a pure 3rd person experience... hell no. With all my heart and strength, no.