I think that the HDD is going to be bundled with Final Fantasy 11. If Sony wants to sell them seperately they need to give people a reason to buy them:
1. Include a web browsing program/email & I.M. (I could care less about it, but people will still buy it just to surf the net on their ps2.)
2. Free downloadable games, video, music. Maybe a place to share and see what other people have done with their PS2 Linux developer kits.
3. Downloadable game content for the more popular games.