Microsoft is planning Xbox 360 game emulation for the Xbox One. You could get the ability be able to play older 360 titles on your next generation machine. Just don't expect the upgrade too soon.
During the Build developers conference in San Francisco last week, partner development lead Frank Savage confirmed that emulation is on the roadmap, but also revealed that difficulties are hampering progress of the plans.
"We’re not done thinking them through yet, unfortunately. It turns out to be hard to emulate the PowerPC stuff on the X86 stuff. So there’s nothing to announce, but I would love to see it myself," he said.
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Unfortunately, no details on how the emulation might work were discussed. Sony will be launching its PlayStation Now service in the US this summer, which will offer select PS3 titles to play through cloud streaming on a variety of devices including PS4, but the fact that Microsoft is looking to get emulation built into the Xbox One system suggests it will be going down a different route.
Whether that means it will allow you to insert your bought games into the newer console for true backwards compatibility, or if it will simply be offering back catalogue titles to purchase online is unsure.
Perhaps you'll be able to continue to play your already downloaded Arcade and full-price titles. And picking up where you left off with cloud saves. That would be our bet.