prudent, and these kind of restriction should not be a problem. More and more people are using dual-screen config, and as ATI/NVidia are the last video cards manufacturers, MergedFB/TwinView configs will be more and more common.
I think it is really unfortunate that NVidia/ATI have been sloppy and uncaring of the requirements of users needing color accurate display on X11. It is not aiding the adoption of Linux/X11 when display calibration is broken for users who adopt these manufacturers solutions. If users want full acceleration for multi-screen and color calibration, they will basically be forced to switch to OSX or MSWindows.
One more thing: I don't think that X is now able to dynamically tell to running applications what profile they have to use, depending on what screen these applications are displayed. So, even if you have a LUT loaded for each screen, this is not enough. Am I wrong?
A convention has been suggested that allows applications to lookup a root display atom that contains the display profile for each screen. This is sufficient for applications to do the right thing, but there is no system level support for handling the different rendering to each screen through the profiles, so it is awkward to do this if (say) a window spans more than one screen. I'm not sure how many (if any) applications are making use of this.