I feel like I need more data on any of these topics before commenting further.
At the moment, however, this decision is one I'm willing to cautiously applaud. Mod chips were a big problem for the, er, 'real' users in the past, at least in terms of running into jackasses with flying Warthogs and submachine guns that fired plasma grenades.
I doubt Microsoft will face 'suicidal' or particularly destructive backlash, and it seems like banning users for violating the TOU is well within their rights. The creation of a shadow Live would be an interesting phenomenon, but my intuition (unreliable, yes) does not suggest that it would be a major threat to Microsoft's operation.
Part of my caution also stems from the fact that this issue seems ideologically and politically sensitive, which means people have probably been through polarization and attitude inoculation already.