There does seem to be a lot of pressure on T3, so starting at T2 seems to be good idea in that sense.
Looking at the TP video it would seem that the plan is for one pier with airbridges perpendicular to the existing building line of T2 and a series of stands west of that which might be walk-in walk-out stands from the low pier or might be remote. The TP website says 85% of operations would be 'pier service level', so my assumption would be that these are walk-in/walk-out stands. The video doesn't show covered walkways to the stands, but I don't think that would necessarily exclude them at this stage. These stands would seem to be ideal for quick-turn operators such as FR - and others.
If FR were to move form T3, significant space would be freed up in T3 for BA and friends, flyBe and AF/KLM to remain where they are. Taking T3 back to its original mission, in many ways.