Originally posted by Clavius -> no advantage over the other FF manufacturers -> no future-proof system -> no solution for all the disadvantages of the K-mount, mirror, ovf, etc... -> no reason to wait for the Pentax FF.
If the Pentax FF is going to be the same old DSLR like the FF's of Canikon that are already around right now, then what would be the reason to wait for Pentax?? Life is way to short.
Taking myself as an example, I already own an FF Canon body that happily mounts all my precious K-mount lenses. The only reason I would see to switch back to Pentax is if Pentax would come with something better then their competitors.
There's not really any better/best as a general idea since people have wants that one camera alone cannot satisfy.
Unless Pentax produce several FF cameras at once, which isn't very likely. Some will want a camera optimised for fast sports action and weather resistance, so AF, burst mode and dual slots will be at a premium, which implies fewer megapixels; others will want something with more pixels for landscape and studio things, so fast AF and burst mode won't be a priority but lots and lots of pixels will be; others will be looking for a simple feature set but a very competitive price to match the D600 or the 6D; while still others are looking for something lighter and more modern, probably without a mirror. Whichever mix Pentax goes for first, some will be disappointed while others are overjoyed. Just as with APS-C, FF only makes sense when seen as a range of cameras, imho.
Since this puts any full Pentax FF programme into a timescale that could run to 3-5 years from now for some folks, if the first Pentax FF camera isn't suitable, I would guess the best thing is either to stay with APS-C which isn't exactly a poor choice, in fact it is staggeringly good by the standards of even a few years ago; wait, if you think you are a generalist and Pentax are likely to satisfy you first; or buy the best FF you can afford out in the market right now if you have particular requirements which existing cameras can deal with.
In this sense, "the Pentax FF camera" is a complete El Dorado. There can never be one which works for everyone.