Sounds like we have a way to get some homebrew games ported into this...
Of course building games and publishing them in a runnable format are two entirely seperate things...
Microsoft has a major vested interest in keeping it a semi-closed platform, and considering that they are going absolutely out of their way with signed binaries and such to prevent people from running non-authorized software (e.g. linux, what not), and that they prevent you from running stuff from recordable media (to prevent 'backup copies') one would wonder how all of that fits in the big picture...
Most likely they'll still charge you your first born to be able to actually *publish* something in a runnable format. Making it and running it are two entirely seperate issues.