The XML? No. The CDN can be mapped via DNS to the Wii U CDN.But is it legal to host these files? I mean, it is code from nintendo. But i dunno.
There is nothing to patch, you would just need a custom DNS server that points the SOAP request to another domain which response with the standard XML. There is no HTTPS or something. I haven't really messed with the update process though and I don't know if the Wii verifies other things (serving custom IOS would obviously not work since they are not signed, but official ones should work).Nice findings, but what we just need to do is replace the old response URL with the new one from WiiDatabase and then patch this in the Wii System Menu WAD, config settings, or anything else.
But since i'm no a specialized programmer/hacker i can't help with that