Well, I have an A7R as "backup". Really, I got the A7R in January thinking it would become my main camera, THEN Pentax decides to surprise us all with the Z. Gee, thanks Pentax...But I had to go for it, despite the (considerable) pain. So then I found myself in my current situation.
The A7R does not play well with UWA or sometimes even not-really-UWA, especially rangefinder styles. It does work fine with "full size" lenses. And now Sony/Zeiss have announced a 16-35 FE mount, and *surprise*: Voigtlander has a new M mount 15 optimized for digital. Just saw some shots taken with an A7 on it from Photokina, and things look promising.
I don't do tele, so I can't comment much on that score, but there are no reported problems there, unless a big honking lens hanging off a small camera counts.
I purchased a discontinued model of a
Rhinocam , mine was only $99 and just lacking a coupe of things the new one has. This allows for use of various medium format lenses including Pentax, and can be used for stitching.
Then there's this, which I will get next year: the
Cambo Actus (I have no affiliation with Capture Integration, but this is just the best rundown I have found). No Pentax mount....yet.
I have been unbelievably busy for the last few months, but in a few weeks my shooting season will start in earnest and I'll be seeing how the A7R and the Z work side by side.