Gaming is more popular now that it was in 1999-2000, to say otherwise is foolish. What is not as popular know as it was back then is dedicated gaming hardware.
In all honesty I don't expect the PS4 to get near PS2 levels, I doubt it'll have the same longevity with so many new smart devices getting release so often, without being the cheapest DVD player for years, without it being possible to sell for less than 150$, without piracy, without Japan and without an insane library of super cheap games and having little competition worldwide.
China is a wildcard, fine, but I doubt PS4 will do all that, or mainly I doubt the Chinese goverment will let it do all that.
I expect 100m, but not much more, I'd loved to be proved wrong.