Edirol has introduced a mixed medai mixer, which allows you to mix sd and hd and vga inputs and up convert and output to HD. It is not a perfect solution, in that you have a SD section and a HD section and you can only feed the final mix from the SD section to the HD section, and the delays in switching in the HD section can be several frames. BUT it does address the needs for live event switching of PC VGA sources and sd sources and HD sources. I think that the main market will be houses of worship that are looking to further integrate pc based inputs (powerpoint etc) along with HD DVD and live cameras., not have to down convert the PC inputs to Video, and be able to output in VGA or HD analog for better projection quality. Not cheap, it is 12 grand US
http://www.edirol.com/products/v440hd/index.html
First solution I have seen, probably will not be the last, the houses of worship market for advanced av gear is booming in the US
Sharynl