I first saw this Rumour from a post of Photo Rumors which points to the source of what Valentin Sama writes at his blog (Google Translated English Page Here), which says that Pentax is going to join the Micro 4/3 camp from what it was told by "very well informed sources".
And then, 1001 Noisy Cameras have made some analyses and sensible guesses on the possibilities and what is going to happen. Whilst those 3 possible outcomes are exhaustive and it will not be going to have four, I would bet that Pentax will not / cannot join the Micro 4/3 myself. Why?
1. Olympus and Panasonic have been worked closely and put much investment on the Micro 4/3 development for both the sensor R&D and the optical form/factor infrastructure and lens development. As such, it is very unlikely for them to let an alien to enter the camp so freely. What is the benefit(s) for Oly and Pana to do so? Don't think the 4/3 and the m4/3 are open systems, in fact these are not!
2. Both Olympus and Panasonic have their own development and design capabilities of lenses and they do not need any of the expertises in Optics which is the only strong point of Pentax. In fact, Olympus is particular strong in optics design (and not weaker than Pentax, I believe) but Panasonic do have the support from Leica. The need with a new alliance for help is surely non-existent.
3. The electronics technologies of Panasonic are much stronger and advanced than those mastered by Pentax/Hoya, whom is just a laymen if compared. So, Oly and Pana has no incentive of any for letting Pentax to play in the game neither.
4. On the other hand, the EVIL (Electronic Viewfinder Interchangeable Lens) market has been somehow congested already and competition has become more and more vigorous with the introduction of the Samsung and upcoming Sony EVIL cameras which even have a larger APS-C sensor (which means better IQ/PQ/high ISO performance). Even worse, the EVIL market also competes somehow directly or indirectly with entry level APS-C DSLRs of different brands. So, why makes the competition even harder to let Pentax play in??
5. Pentax themselves simply have no more resources to make one more completely new line-up with new bodies and lenses of a new form factor. They now have the soon-to-be-released 645D and the current APS-C system (which possibly be softly migrated/hybridised to an APS-C/135 FF system like the C and N's ones (and what C and N did before). Those two have already put too much stress on Pentax/Hoya already for their limited capability/capacity for finance, R&D and production as well.
So, all the above facts just tell me that Pentax is not going to have a Micro 4/3, no matter they want to have one or do not want. It is just too difficult for them to have one, or, just almost impossible! And, what's the benefit to build a Pentax m43 (system) at this moment? Nope, I would say! The Pentax K-x has been doing well for gaining new market share and Pentax has done no worse than Pana and Oly alone. In fact, Pentax has not announced any new DA (APS-C) lens for almost two years now (but surprisingly just a new 135 FF lens, the DFA 100 WR). With their much limited resources, I think they will still continue to put those already much tight resources on APS-C and FF DSLRs and system (secretly for the FF) until some days they have secured the market share somehow and survival is ensured before they take more risks and enter into new area(s) without good reasons and/or supports.
So, rumours are just rumours, just believe it or not. Time will tell if the rumour will come true or not and I will be right or not, on the other hand. ( But I always encourage you to look back at my past track records on the hit rate of those of my judgements on rumours and predictions in the past, and you will know! ;-D =V= )