Alt + Tab behavior may change slightly

It is also possible that this will be done in the next update.

Windows 10 Insider testers are already working in full swing on the so-called Sets feature, and as a result, it's very likely that the Alt + Tab combination won't be able to keep its current form. 

There are certainly several of our readers who haven’t heard of Sets yet. The basic idea is not revolutionary, it nonetheless seems like an exciting opportunity; Microsoft brings long-proven tabs in browsers into windows. According to the current plans, Alt + Tab would no longer switch between program windows, but would scroll through the tabs.

As mentioned above, Sets could ideally debut in the fall update (1809), but that’s by no means certain because Microsoft wants to test the feature very thoroughly.

Source: ghacks.net