Nice thread. A couple of questions for you.
Are you suggesting that games be made to work for both the original 360 specs and these enhanced ones? Perhaps a few that are enhanced only? This could be an issue with developers unless MS develops software for easy development and handling of the two different sets of game assets. This would not really be an issue for first party 360 or third party PC/360 games, but console only multiplats would probably not utilize the higher end specs of the enhanced 360s unless Sony released a newer console or enhanced specs for the PS3 as well. Perhaps it isn't an issue.
What possibilities with Natal will the current 360 specs not be able to handle?