So now we're quite likely down to three monster alliances (DL/NW/CO, UA/US and AA) and maybe some loose partners like AS, HA and HP.

As a customer I'd be thrilled if I could get miles on any airline credited to any other, except that there will come a point when consolidation will kill competition and the results then will definitely NOT favor the customer. Mileage devaluations and other customer-unfriendly moves will be done in lock step (i.e. collusion, not competition). I hope we're not about to reach that point.