What Pentax needs is a smaller, lighter camera. If mirrorless is the best way to get the size and weight down (while keeping the APS-C sensor size), then so be it. But they could also make a smaller, lighter dSLR if they wanted to.
The FujiX-Forum has MANY members who came to Fuji mirrorless cameras because they don't want to lug around their big heavy Canon, Pentax or Nikon dSLR kits anymore. Some Fuji-X forum members sold their dSLR gear to pay for their new Fujis - others kept some of their old dSLR kit, but they are now spending their money on Fuji gear.
Other potential benefits of the mirrorless design are: fewer moving parts, quieter operation, no front-focus/back-focus issues, and WYSIWYG electronic viewfinders. The downsides of mirrorless designs are shorter battery life - due to the electronic viewfinders - which also tend to be smaller and fussier to use compared to optical viewfinders. For me, the tradeoff is worth it.
A lot of people mention Pentax as a "niche" player, but I don't see why their niche should not include a travel camera which is somewhat discreet, smallish, and lighter in weight, built around the APS-C sensor. I really don't care if it has a mirror or not.
Back in the film era, Pentax agressively marketed the MX and other "M" series cameras and lenses as smaller, lighter and more compact than the competition, so to me, that was part of their niche, and still should be. <
see old MX advertisement, click here>