Well, the first thing that will go is the division that is losing Sony the most money, in which it'll be its TV division since it's still technically owned by the company. Smartphones will be next. SCE won't be spun off because it's doing well financially.
How profitable is SCE at the moment? I mean, I know the PS4 is doing well, but you have to factor in PSV, too. I had a bit of a look, and apparently the forecast (from July, not the updated one now) has "Game & Network Services", which apparently contains SCE, is at 25 billion yen, or about $230 million. For comparison, their camera division was forecast with 38 billion yen, their "Devices" division (looks like it has sensors, power supplies, etc) with 51 billion yen, their Pictures division (movies, TV shows, etc) with 65 billion yen, their Music division with 48 billion yen, and their Financial Services division (apparently there's a Sony Bank, Sony Life Insurance, etc) with a whopping 164 billion yen.
And their 2013-2014 result was a loss to the Game & Network Services division, despite the huge launch of the PS4.
So I don't think we can honestly say that SCE is doing exceptionally well, financially (at least, not its entire division - I'm assuming that there's more than just SCE within Game & Network Services). Obviously, without more information, we can't be certain, but it doesn't look like SCE is a particularly profitable division.