Not worried about playing one retail disk at the all at the same time. The ones that do get alot of playtime in my house, I buy 2 copies. Call of Duty series is the only one I buy 2 of. Also have 2 copies of GTA V pre-ordered, since I suspect will get alot of use. I suspect we haven't heard the last of this from M$. I just don't see how they expect people in the same position as me will shell out 2, 3, or more times the retail price to play a single game in the same household.
I really think you are the innocent causality in their war against used games. They don't want gamestop making the profit they would otherwise be making if they just blocked used games like PC does. I just don't see how they can block used games and still keep multi-xbox families happy. They could allow you to link say 5 gamertags on a family plan where one license would be good across the whole plan. That would stop their used game problem and still allow people like you to do what you want. This would create on obvious new problem though. Now friends and family in multiple homes would start linking their gamertags. Suddenly every time one person buys a game the other 4 have access to it for free. That is why they won't allow multiple accounts to share games.
In reality there is probably a small percentage of people who have multiple Xbox consoles and gamertags in the same household so they probably don't care. They can make millions more by cutting out gamestop and they will piss off a small number of people by doing it.
Maybe you will have better luck with whatever Sony decides to do. If they are allowing used games I wouldn't expect that to last either though. If they see that Microsoft is successfully doing this and it drives up their profits they will follow suit. People will be mad at first but eventually that will just be the way it is. If it is the same across PC, PS4, and Xbox people will have no choice but to just accept it or quit gaming.
I don't buy use games but I am upset that this means gamefly most likely won't work for the next generation. I think we all saw this day coming though. You don't buy software anymore. You just buy the license to use it. Buying one copy of Microsoft office doesn't enable your whole household to use it. If you want it on all the PCs in your house you need a license for all of them. This is just the same thing making it's way to consoles now that they have the technological ability to do it.