From what I've read on XBH, it seems you only use the serial port so as not to have to burn a new dvdr dl every time you'd like to test your homebrew. I'm no coder, but from what I've read it looks as if you won't need the serial adapter very soon. Once someone can find a way to install a dashboard, which from the looks of things is very possible, you'll only need to burn off your backup of King Kong with the dash installer on it, and then it's headfirst into homebrew fun.
I can only imagine what will come of homebrew on the xbox 360. Perhaps finally a DC emu? PS2 even?
For now, I guess, we leave it to the pro's to tinker and exploit their hearts out.