Depending on the release date it could be their hybrid system. X is used by Japanese companies as "Cross" (Think Street Fighter X Tekken and Project X Zone), so it could be that. However, a hybrid system should come out in 2017 or 2018 because that would fall in line with the expected end of the Wii U and (New) 3DS's lifecycle (Wii U being 5-6 years and 3DS being 6 to 7, which is similar to their other systems, such as the DS, Gameboy, and every home system). However, it's status as a 3rd Pillar implies an earlier release date, but a hybrid wouldn't be good for the Wii U. This is all very interesting, and I can't wait to hear more about it, probably at E3.
I just hope that by Smartphones and Tablets, they include Windows Phone, 8, and RT. So many apps skip out on the Windows Store it's not funny. I am speaking as the owner of a Surface Pro 3. I also hope that the PC section is an application and not just a website. If you're going to have an application for an external device, you have to make it available everywhere. I'm talking iOS, Android, Windows Phone, OSX, Windows 7, 8, 10, Linux, Chrome Store, and anywhere else possible. Get this out to anyone and everyone.
They mentioned PC. So I assume Windows 8/10 will be supported.