You might be the first ...and someone always has to be the first.
Try it and let us all know.
FWIW : I would be sceptical of the possibilty of success and the value of trying it.
But best of luck to you.
That will be interesting...
Color and FCP have a very interesting relationship. I suppose you'd need FCS installed to have Color on-board anyway, so you'd have FCP available to convert the XML you exported from PPro CS5 to Color.
I'm not sure how the project conversion would work...I suppose you wouldn't want any effects or manipulations on the timeline where PPro and FCP have agreed to disagree...and I assume all the limitations about any existing effects being stripped, time-altering motion being either rendered (and therefore, no longer "RAW") and having the completely flat, one video layer timeline caveats that exist in the typical FCP>Color workflow will still exist.
If the files didn't take up so darn much space, Premiere Pro CS5's capability to work directly with (or export) DPX image sequences, and particularly for working with over-range colors and writing them into deep color-precision DPX files would seem a completely appropriate way to get into Color directly and bypass FCP entirely if you used it as a "finishing" pass.
PPro is the only editing app I'm aware of that can work in 32 bit float color...but I think you're stuck going through FCP if Color is your tool of choice, and you want to access the R3D files directly.
I'd be curious to hear how it goes.