I think it is possible that Windows 10 or Linux would be used on most or all gaming handheld consoles in the future because there are already many PC games which are compatible with Windows, and Linux. There are also many PC game programmers, and workers who know how to make games for PC.
Convincing existing PC game developers to make games or port their PC games for a handheld which uses Windows or Linux maybe easier than a custom operating system like the Sony Vita and Nintendo 3DS OS made for handhelds, or mobile operating system which may change a lot over time, or become discontinued or dying like Firefox OS, Web OS, Symbian, Windows Phone, etc.
Convincing existing PC game developers to make games or port their PC games for a handheld which uses Windows or Linux maybe easier than a custom operating system like the Sony Vita and Nintendo 3DS OS made for handhelds, or mobile operating system which may change a lot over time, or become discontinued or dying like Firefox OS, Web OS, Symbian, Windows Phone, etc.