Apple will not enter the Video game market directly. Only indirectly (Iphone, Ipod). It doesn't fit their business model (Make high priced, well designed, live style products).
Ever seen a high priced gaming hardware make a good profit? This buisnes model doesn't function on the gaming market. As seen by the action of Apple there are already problems on the mobile phoning market. And that's a market where I would say, their business model fits better.
Sega could of course, but I think they will not. Just to risky for their current cashflow.
EA is a possibility, as other have said. They have the cash flow, have the development power to drive sales. But the new CEO doesn't seem to want to take such high risks right now. He is concentrating to make profit on the current software, and change the way EA is doing business. I wouldn't rule them out, but that is something that will keep them busy for at least another 2 years. Making an entry risky, because you give something like that a lot of attention in the beginning.
I want to add AMD and Intel. Both know how to produce such hardware. Both produce CPU and Graphicchips. They could build the hardware perfect in a technical matter and damn cheap. If someone wants to enter this market, it has to have on the hardware front a better business model than the current producers. Both just could take chips already produced in high quantities and therefore make better prices (and profit on hardware). But both would have problems on the Software side.
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