Its possible, but I think it is unlikely ...
In my opinion neither Sony or Microsoft are particularly imaginative companies, and they tend to be able to produce evolutionary products rather than revolutionary products. Sony was able to "come to power" in the 90s because Sega went out of their way to alienate their customers while Nintendo decided to offend third party publishers; in other words they were in the right place at the right time.
When you're dealing with products that are developing in an evolutionary way Sony or Microsoft are highly capable of maintaining or expanding their marketshare, but when these products are developing in a revolutionary way they tend to get decimated; Look at how Sony and Microsoft dealt with the iPod, Nintendo DS, or Wii to see what I mean.
If Sony and Nintendo screw up Microsoft would be able to gain rapid dominance, or if the market develops in an evolutionary patter for a long time they could slowly grow their support; but I think it is unlikely that both Sony and Nintendo would screw up at the same time, and this industry tends to have periods of evolutionary and revolutionary growth.
