Most of the above ideas are variations of what already exists, such as a faster lens, a digital body, a focal length between x and y... but I would love to see something that no one else makes for any RF camera: a dedicated soft-focus portrait lens. Say a 60 or 75 mm lens with intentional abberations to give a pictorial effect, not unlike a Thambar (although I think 90mm is a bit tough to use in RF).
Mostly one needs to shoot LF to get to have fun with such lenses. I blew $1,500 on my 9" Pinkham and Smith and consider it a steal as the effect is unbelievably beautiful. It's only a meniscus-type lens, so how much could it cost to produce? Cooke re-introduced an SF lens (also 9") a few years ago based on an old P&S lens, so why not make such a beast for RF photogs?
One of my main reasons for shooting LTM is to use the funkly old Leica glass. I love what Mr. K has done and I have a few of his products, but why not introduce a new lens which would give a seriously "olde" time look to our images? In other words, instead of competeing with Leica or Zeiss for the sharpest, fastest, widest (whatever) lens, why not bring back a really old design for a completely different look?