Microsoft apparently working on a light Windows 10 version
Microsoft seems to have some long-term plans for the Windows platform but, as it usually happens with such plans, everything changes as time passes by. These being said, you should be aware that all the information below should be taken with a (very large) grain of salt for now.
According to a report from Petri that has been recently quoted by Windows Central, "Microsoft is working on a new Windows 10 SKU that is being internally referred to as Cloud Shell" and "it sounds like Microsoft is building a new edition of Windows 10 for lightweight devices, similar to the Surface RT."
What Microsoft might offer in the coming years could be Windows 10 Cloud, a full desktop operating system, but since it is expected to support ARM as well, it would not be such a big surprise to see that the new operating system is, in fact, Windows 10 Mobile for ultrabooks and tablets.
Windows Central thinks that Windows 10 Cloud is set to arrive later this year, so we should just wait for more leaks and rumors. If it is scheduled to arrive before the end of this year, the first official bits of information should start to surface quite soon as well.