I happened upon this thread and thought I would add my two cents. Hope this is useful and not a "me too" sort of deal.
I have a IIci that I made out of two IIcis, and I was thinking the same thing--I would like to use say a native resolution 1280x1024 Sony model SDM-HS73 TFT LCD with it--it's a straight analog VGA LCD, circa 2003 technology. The IIci I put together now sports a Macintosh Display Card 670--no great shakes but it takes the load off the 8MB on the motherboard and offers some resolution options. System 7.1. I got a Griffin Mac PnP adapter and gave it a try.
By the way, the Griffin Mac PnP Quick Reference Chart is here, in case it's difficult to find--it took me a while and I was fiddling in the dark until I got it:
http://www.griffintechnology.com/manuals/0000/0024/Mac_PnP_Instructions.pdf
I set the DIP switches to 5,6,7,8 on, with the Sony LCD plugged into the Macintosh Display Card. I kept a Apple High Res Monitor plugged into the on-board video. The Monitors Control Panel recognized it as a 21" Apple Monitor and pushes 1152x870 at up to 256 colors. The SDM-HS73 was able to resolve pitch issues through the menu, and through color temperature settings you can get that very nice platinum grey System 7 look, and it scaled that 1152x870 very nicely--after all, 1280/1024 is 1.25 and 1152/870 is 1.32, not too far off.
I'm going to keep my eyes open for a video card that can push 1152x870 at 24-bit color, though I'm in no big hurry.
So, my recommendation is to get some kind of 1280x1024 native resolution LCD monitor and a Mac PnP and give it a try. I'd try VGA first (DIP Switches 5,7 On), then 13"/14" RGB (DIP Switches 6,8 On).
Best,
John