In another 6 years, if Nintendo keeps on selling it so long, it would be easy. In another 5 years if its late years sales drop is small enough (and this could happen even more easily if Nintendo releases Wii2 late). In less than another 5 years it's quite difficult, not impossible, but hard.
Anyhow, Sony will keep on selling PS2 as long as sales hold, to make it as hard as possible for Nintendo, PS2 image is important.