"Consolidated loyalty" is an oxymoron. At that point, frequent flyer programs are just another form of Green Stamps. There is no reason to fly on a particular airline since you can earn on one and burn on another.

The same goes for elite perks. If I have channeled my business to Delta (which I have) in order to become an elite flyer, it is not fair to have the benefits distorted by members from a larger or smaller airline flooding (or getting flooded, respectively) the system.

If two airlines actually merge, then you can deal with the new company's frequent flyer program as a single entity and can mine the data to come up with the appropriate elite tiers/perks.