Such a solution already exists for big-box Amigas (with A2000 being the exception), and it's called the Mediator bus board. Yes it may cost a lot, but I think it gives better value for the money than old Amiga graphics cards at insane prices (like you mention here).
We can say the same for not only video cards, but for NICS, USB, Sound cards, etc. The X-surf-100 did well and the Prism sound card also looks to be a good success for a zorro bus.
I would like to buy a high end video card that even uses tricks like the roxxler, a Zorro Bus card that redirects amiga video to DVI/HDMI would be a hit.
Unless a Grex type solution that gives benefits of another bus, zorro is good solution, IMHO...