I do not agree that the older Pentax film era lenses don't make sense on 33x44. Most of the film era Pentax 645 lenses are actually lighter than the later DA models designed for the smaller digital sensor. Compare the 120mm Macro (700g) with the 90mm Macro (1000g, albeit with SR). The modern 28-45, as amazing as it is (and if anyone wants to see some
full-width samples I posted some here), weighs 1500g, which is over 600g more than the older 45-85 FA, for example (I know this is apples to oranges, but you get the idea).
I think the greater weight of the modern DA lenses is the fact that the digital sensors are exceedingly demanding and the new lenses have a lot of glass in them! Make no mistake, however, many of the older lenses are very good indeed. My 35mm A is astonishingly good and weighs less than 500g. The 75mm FA is sharp as a tack and weighs just over 200g and takes a 58mm filter! Quite frankly, you'd have to be window licking mad to pay five times more for a super duper DA version of the same lenses when some of the legacy lenses are still so good on the 645Z. Maybe a future 70MP sensor will be more demanding, but right now the existence of so many good quality affordable legacy lenses is one of the main selling points of the 645Z IMHO. They're not all great and there are some real dogs, but a bit of research is rewarded with huge savings.
As a point of interest, if you scale up the 42mp sensor in the A7R II to 33x44, you get 71 MP. At this point, as long as the lenses can keep up (and I have no doubt the best lenses will), further increases in MP will make absolutely no difference to how good you 50" prints look to the majority of eyes and so I feel the 33x44mm sensor will prove just big enough. Sure, bigger formats will go higher, but whether mortals have any need for it is debatable.
