Windows 10 store apps will be limited to 10 device installs on the same Microsoft account;

[Windows Central]

Windows 10 apps from the universal Windows Store can be downloaded and installed on up to 10 devices per Microsoft account. That's the word from Microsoft's own store documentation, and it's a big decrease from the 81 device limit that is currently available for Windows 8 and 8.1 apps.

Full story from the WindowsCentral blog...