Chief:
My instinct is that it boils down to you guessed it, money. I don't think the owners are much interested in separating themselves from the land. There is very much a preservation effort going on in Raymond. Please checkout "Friends of Raymond", non-profit corporation dedicated to preserving the battlefield. They are affiliated with Friends of Vicksburg in developing an entire Vicksburg Campaign Trail. Just this past weekend I went to the dedication of the "Generals" marker. Walking trails, interpretive signage. About as good as it can get for a bunch of locals to develop there own battlefield park.
I'll make some calls tomorrow and see what the status is. Although I doubt there is anything on the radar for the Coker House.