Front loaded, much like modern blockbuster software. I don't think the PS4 will have any shot at Wii-like numbers, certainly not above in weekly sales, the Wii sold about 16.5 million in its first full year, followed by about 50% up yoy in 2008 and then down 15-20% for two years and the rest we all know.
I think a lot of people are getting ahead of themselves due to the massive launch figures, "PS2 era" and other sentiments are simply premature and out of place; there is no way any console will dominate like the PS2 or sell as much in the foreseeable future. With this likely being a shorter gen than the 7th, there's just not enough time to reach any amazing numbers. I'll be truly surprised if the 8th gen roster of home consoles manages more than 160-170 million consoles combined and handhelds will likely be below 50% of the 7th gen.