If there's ever going to be "mod" tools for BF3, at most I expect that you can
1) change skins (but not underlying models)
2) tune the weapon damage, blast radii, armour values, amount of HP and such
3) make new maps using only existing statics, weapons and vehicles (and even this is unlikely)
Anything else basically requires that you would run the stuff through the third-party animation engine compiler, physics engine compiler, particle engine compiler, and whatnot, and DICE is not going to be able to licence those en masse to end-users. If they had done everything in-house in the style of CryTek, maybe then you could get a "BF3 SDK", but alas, they didn't.
tl;dr: even if mod tools were released, expect that minimods in the style of the earliest releases of PR might be possible, but PR as is sure isn't. As for total conversions like FH2 or Pirates, no way.