One problem with this approach, and to some extent with server-side in general is that all these processes can bog down your server really quickly.
R is even slower to load.
Even so, the processing requirements will be greater than for serving HTML or JAVA programs. I remember trying to use a server-side demonstration of Penrose tiling from the wrong side of the Pacific. The Pacific link is rather faster than your average modem, but it was still painfully slow. While server-side has lots of advantages I think it would be really useful to have a technology that doesn't require so much from the Web publisher. A major project such as the UCLA textbook can justify this sort of processing power but it might easily be out of the range of a department producing web-based course materials.