Thank you all
All this is great info. Much appreciated
After some additional thought I did edit my first post today as I might add also these two Mk papers: the Hahnemühle Museum Etching 350g and the Ilford Galerie Cotton Artist Textured 310g. But in much lower quantities that the Pk's, like a third or even a quarter of the Pk's.
Some feedback:
@mearussi: good point about bugs and operational data. Waiting for the first P900 reviews and real users feedback is therefore good advised. I guess waiting two or three more months is not a deal breaker for me (as long as P800 will be still available then, one can hope, right).
@gkroeger: Thank you for the info on the possible ability to load these fine-art papers through the top sheet feeder of the P900. As you said that it's not yet clear as you found discrepancy between the Epson's sales literature / online videos and the user guide I hope the first reviewers will clear this topic for us.
@unesco: I think the pizza wheel marks and the Black Enhanced Overcoat mode are another topics for the first reviewers. You are right about my portraits, they don't use highly saturated blues/violets.
@Chris Kern: good point about the possibility of resolving the fine art paper-feed problems with the P900.
My conclusions so far:1. Print quality
The P900 in theory has a slight advantage due to slightly larger gamut (added new Violet ink) and the Black Enhanced Overcoat mode. To be proven in first reviews if relevant to my work.
2. Pk / Mk switching
The P900 has the advantage due to no ink switching. But for my use case, now adding also the Mk papers in lower quantities, occasional Mk / Pk switch of the P800 is not a deal breaker.
3. Fine art paper sheet feeding
Unknown. However, in theory the P900 could have the advantage. Needs to be verified in the first reviews. I think this will be the deciding factor for me.
The one that better handles my chosen papers will be the winner for me.4. Ink cost
The P800 has the advantage. I think this is a very subjective decision, however. At this point the difference in ink cost due to lower ml P900 ink cartridges with higher per 1ml price is not a deal breaker for me.
So far I am more inclined to the P900 with my greatest concern being the fact that P900 is still unknown. As @unesco said "Might be a breakthrough or a disaster." Will now wait for the first reviews of the P900 to be published.