Not "want" you say... well it would just have to have a poorer library of games compared to it's cost than the next Xbox. Unless they price it at £500 and the Xbox is £250 I am doubtful that will happen though, because Microsoft doesn't really have any first party games whilst Sony does have at least some desirable franchises.
Your question in the body of the OP is different though, there you are asking what could Sony do that would make me not buy it... for which the answer is price it above £100-150 (where it lies in that boundary will depend on how much the Wii U is) There are other factors of course that may move the price limitation, or something like anti-used game tech/always-online bullshit/subscription for online would probably put me off entirely. This is still assuming the PS4 has a half-decent game library.
As it is I currently have no plans to even buy the Wii U, but if I do decide to join the 8th gen most of any decision I make regarding me buying the PS4 rests in Nintendo's hands... in other words Nintendo will have to really screw up the Wii U for me to look at the PS4 first.
