The possibility that the spec could change since it's not finalized, not to mention: do you even need it? Your internet speed will remain the same, you're probably not going to see much of an increase in response times, 802.11n can cover ranges in most houses, and unless you're doing massively huge transfer over the network constantly, you're just wasting bandwidth. Especially if the number of connected devices on the network is only a handful.
The house I'm in still uses an old bg router. I haven't felt we need to upgrade for speed, it's mostly because the damn thing feels like it's on its last legs.