Shakeout in the mirrorless market

The win for O/P:

It adds credibility to M43 (not that it needs a lot more, but every bit helps) without seriously denting sales for either. Pentax is not a large company, and doesn't have a huge distributor network or customer base.

With those three cooperating, just having three very good companies to choose from, with the same lens mount, really makes the Sony, Nikon, and Canon efforts look so... proprietary. You have a chance to really hammer the big two in this fast growing market before they even get going. Opportunities like that don't come along very often.

The win for current M43 owners:

Pentax would bring it's prowess with pancakes and primes. They can fill in the gaps that haven't been attended to. DA Limited is very high grade glass.

This would bring a third sensor option - doesn't Pentax use a Samsung produced sensor? Pretty good one, judging by the K5II.

The win for Pentax:

Ready access to a market that's clamoring for high quality glass. The body... let's see what their sensor can do against the best from Sony and Panasonic.

Give it some thought, O/P... you gain more than you lose, and you can relegate Canon and Nikon to 'they also serve' status for a long time.