MS is the most likely to bow out, but Sony is a possiblity due to their business model of selling consoles at a loss and recooping cost through game sells. This model becomes a disaster if you can't sell enough systems to make games profittable. I'm not saying that'll happen, just it's possible.
It'd take a brave (or foolish) company to step in and they'd have to believe they have some novel twist (like a wiimote) that'd take the industry by storm. They also need deep pockets, IPs and recgonizable brand.
Apple is a possiblity as mentioned previously but lack any IPs to start. Also American companies sell poorly in Europe and Japan. However, Apple could possibly leverage existing relationships to obtain exclusive IPs.
My favorite choice though is Virgin. Wait, I'm not crazy, here me out... We all know Virgin for airlines, but Sir Richard Branson is one electic guy and Virgin has a huge catalogue (http://en.wikipedia.org/wiki/Virgin_Group) of subsideries including comics, music, online games, movie studio (now closed), mobile phones and mobile games, books and so on. Branson has the vision, balls, money and exisiting IPs and infastructue to give it a go. The Virgin brand would sell equally well in Europe and NA, but still struggle in Japan unless it was something totally unique and to their tastes.
