Fragmenting the playerbase isn't really good for anyone. Nonetheless, we've survived Co-Op being added... there are players who prefer the mode; I suspect there are fewer 'dirty tricks' played by the bots.
So... keeping Scouts out of the conversation, if there were three levels of play, where each level had certain elements of the game added as one climbs tiers (and maybe a tutorial to explain the mechanics/dimensions added for new tiers) would help?
I, as a nosebleed-level MMR player (compared to a 1700-MMR player) would not want to play in a server without stealth, EOC, turrets, orbs, detonators, and with radar ranges on the order of Assault. This leaves core gameplay - positioning, leading, burst explosion reflection, and dodging. Take Siege out of this level, too. If I were inclined to create a new Smurf, I'd have to suffer here until 1700 MMR - about nine games.
Say a 1700-level player can then graduate to servers with Stealth (Infil/Pred), deployable items, and latent primaries (EOC). He can stay in this level up to 100hrs gameplay, or drop back (and live with the restricted gameplay). No one over 100 hours can join the first level, no one over 100 hours and 1900 MMR (both conditions satisfied) can play in the second level. A skilled player can introduce 'dirty tricks', which will run rampant in this level, until players 'wise' to them (learn to check radar, maps, positioning). You limit the mayhem a smurfer can create by keeping orbs, and certain internals out of this level (cough 'extractor', 'fuel converter', 'repair kit', cough).
Private servers and Mayhem remain wide open. Top tier has all things Hawken.
Just a proposal. I would live with nodelocking an account to a PC and limiting two per PC (motherboard/drive EID) for smurf control if it would save Hawken.