Yup. I knew about the U-Verse thing and I've heard statements from XBOX 360 owners that were amazed to find they could simply plug their XBOX 360 into the U-Verse converter box and go online.
I'm guessing it's not quite the same as the scenario I suggested.
With U-Verse, there is a device that acts as your home gateway. If I understand correctly, it connects to your home coax cable splitwork and the U-Verse set-top boxes get video over IP. Because the STB already uses an IP connection, it's trivial for engineers to add a functional ethernet jack.
With most cable converters, IP traffic would have to share the same cord with other types of transmissions (QAM cable). With U-Verse, it's all IP anyway. It would work even if you only had a single U-Verse set-top box.
If this works with the new cable boxes from Cisco/ScientificAtlanta, I'm sure it would require at least two converter boxes. One STB would connect to the XBOX 360 with a network cord, and one in another room would have a network cord going to the LAN port on a router or modem.
I don't know if I'll ever have a chance to test it. I don't use any converter at home. I just have an HDHomeRun Prime tuner (cableCARD) connected to my network and I use Windows Media Center.
The "Home Gateway" is just another router with an HPNA bridge built in to it. If the cable STBs have MOCA bridges built in to them, you don't need the other one. You'd have one STB where your router is plugged in to ethernet and then over coax, it'd send both the MOCA and the TV signal to the other STBs which would demux the MOCA from the TV signal.
You're overcomplicating the setup. MOCA is a simple bridge, that's all. It doesn't have any real logic or programming or anything like that.