Interesting questions, but I think many are already dismissed.
1) As noted by another poster, MS is greatly increasing the backbone to handle this immenent surge in demand. I believe the capacity their adding will reduce the risk to the point it should never become an issue. MS seems to be plannning for this potential risk already.
2) Yes, to expand the system to solve #1 there clearly is a growing cost on their end and there is a concern for cost increase on the user end. However, that may not be in the form of XBL price increases, but part of what apears to be the cost of games increasing and especially the new DRM policy that will surely gain new revenue stream for MS.
3) This is really a non-issue. The servers for this will never be turned off. This isn't the same scenario as online multiplayer support. This more of a generic set of SDKs to handle similar processing for all games continuously going forward. However, even if it did turn off, MS already said what would happen and all it really comes down to is longer loading times and potentially a hit on frame rate.
4) Answered in #3.
5) Partially answered in #3. It won't affect porting at all. MS is handling where the calls to its SDK are going, not the developer. (IMO) So, the devs / engines are the same, but one of the XBone's OS layers is making the decision to handle a particular process in-house or sent to server.
