None of all this is going to happen.  Miners want small blocks and a fighting fee market.  The cartel you are talking about with large blocks only sets in with such incredibly large blocks, that they are out of the question in the next few years ; if you want a mining cartel, the telephone between mining pool bosses is a much more useful device than multi-GB blocks that saturate small miner's network links and most of the user nodes.

Bitcoin is already centralized, or on the brink of being cartel-centralized.  Come on.  5 guys have more than 50% of hash rate under their control.  10 guys, more than 75%.  The only thing that keeps bitcoin still "decentralized" over these guys, is their mutual understanding that they shouldn't show public agreement ; and maybe their egos.  This is why they fight or mimick to fight.

I love that mining pool that dedicated 75% of its hash rate to BU, when BU said that they would fork at 75% hash rate.  Giving 75% to BU is the perfect move to do if you want status quo.  BU rises, you lower ; BU lowers, you rise. 

Miners want status quo.  All of them.  So they mimick divergence in opinion, which makes you believe bitcoin is still decentralized over 10 guys that can't agree.