I agree that leaving a permanent position for a 2 year contract is undesirable and carries it's risk. But staying in a permanent contract with an airline can also be considered a risk, whether it be job security or career development. That can only be assessed by the interested party.
I don't foresee that easyJet will not take good experienced crew permanently at the end of the fixed contract period. The contract will probably be structured to become permanent after two years from the outset.
As for time to command, it changes on a yearly basis so impossible to say but on average easyJet does about 100 command upgrades a year. I'd say five years is a reasonable estimate right now.
It's far from great (paying for rating, contracting), and I'm just trying to help those interested with their thoughts, but the rewards are good. Alexander de Meerkat is right. On a permanent contract, easyJet is a very good place to be.