First read again this concept as previously proposed by a Pentaxian:
http://ricehigh.blogspot.com/2013/07/pentax-spotmatic-digital-concept.html
In fact, Sony has made it close with the A7/R and Nikon now has achieved that exactly with their new Df but unfortunately it is not a Pentax! >:-(
Like all the Pentax APS-C flagship, the FF Nikon Df is also weatherproof:
And, how much is that new Nikon retro-look 50/1.8G lens sold? It is about $250 for comparing the list prices at B&H (here and here). This lens does have a distance scale. For the same listed price, we can also get our DA50/1.8, which is just a pure "plastic wonder", however! :-o