It could go either way next gen. Nintendo was largely irrelevant after Gamecube but then shot back with the Wii.
If Sony push the Playstation brand by actually make use of their TV business, the acquisition of Gaikai and their wider departments then they could at the very least stay as relevant they are now. However, we've seen how Sony can have big ideas which never fulfil their potential (Xperia Play, PSP Go) so it really could go either way. In the handheld space they're largely irrelevant already.








