The Pentax Rumors article is interesting but frustrating in the way it is written. Apparently, "Fuji was one of the names that was mentioned", so what were the others? It sounds like the writer is being selective in what they choose to pass along, and trying to shape the story to their own interest. There are many kinds of collaborations. It could be nothing more than a lens manufacturing relationship where a manufacturer designs and makes the lens for the camera maker, like what Tamron does for Ricoh, or what Konica-Minolta does for Olympus and Leica. The assumption made is that it is to share new, large sensor, professionally oriented mount system with Fuji, which seems a bit odd when you think that Ricoh has just made a big gamble on a professional DSLR market. My guess is that the most likely move into mirrorless would be something similar in focus to the GXR system under the Ricoh brand. If they work with a partner, the most likely way would be for sourcing sensors, lens or some other component.
I'm still surprised that Ricoh lists GXR in it's current product line-up on the Ricoh Japan website.
Products | RICOH IMAGING
That list is otherwise quite up to date, so it's hard to believe it's just a mistake. The 645D, K-3, GR and other older models have been removed, but the GXR is still there. You haven't been able to actually buy them anywhere for years, so I'm really not sure what they are trying to say by keeping it there. Are they trying to leave the option open to make a successor one day?
I still think the GXR was a fundamentally good concept that suffered because it was a bit ahead of its time. It would be more feasible now that we have one inch sensors (ideal size for compact zoom modules), and now that APS-C sensors seem to be very cheap to source. When you look at fixed-lens cameras, They are a lot more popular now than five years ago. Sigma now makes its DP cameras in four focal lengths, and Nikon has just come out with three expensive zoom models based on one inch sensors. Canon has an even bigger line-up. A fully developed GXR system could be all of that, plus having K and Q mount modules to integrate with their other systems.
I know this is highly unlikely to come to pass at this stage, but I like the idea and I think the Fuji collaboration is no more probable.