I don't think I've ever seen a HDMI mod that requires an alteration to the original hardware. Adding a HDMI port directly to the Dreamcast sounds great for ease of use, but it would probably take a lot (time and money) to get that done. I prefer the GCHD Mk II HDMI solution for Gamecube. It works perfectly, and no hardware alterations are required.
This does look good though. I've been kicking around the idea of re-purchasing a Dreamcast. I was actually reading about various Dreamcast HDMI converters just a few days ago.