If the next X-box is online-only, Microsoft may well have shot themselves in the balls. From what has been previously announced, the PS4 is not, and the Wii U sure as hell isn't.
Gamers see always-on connections as nannying, as the company watching over your shoulder to make sure you're being a good boy, and that's probably because that's exactly what they are. They're also a system of planned obsolescence, as the game can't live without the service, and they're a way of taking more and more private information from the end users, to be sold and used for more and more invasive advertising.
In short, online-only can continue to fuck off, and if the next MS console is online-only, a great many of their fans may say the same. It is far more likely to boost sales of the PS4 than the console it's designed for.