Our little set of APIs let you integrate your Add-in into the Home Server Console and interact with some of the elements behind the solutions we provide. But all the interesting work that great Windows Home Server Add-ins will do will be done using the standard “Windows API”.
This is a smart decision on Microsofts part for obvious reasons. WHS seems hopeful as is, but with the help of third party developers, it could become a much more robust server OS. The SDK is available now, but will only do you any real good if you are have access to the beta.
Source: Home Server Blog