Well, in that case, the only thing for it to do would be to introduce PS3 in such a manner as to make users' future upgrade path to this new, aspirational system clear, but without actually positioning it at a level where they're likely to abandon PS2 en masse - flooding the market with second hand PS2 consoles and software and essentially wiping out the long tail business.
This is, obviously, an extremely dangerous game to play, and for Sony's sake I rather hope they've got some aces up their sleeves for when the going gets rough. One such ace might be pricing, because it strikes me that the PS3's high price might actually be rather more transient than Sony would currently have us believe.