Future sight or whatever aside, I think it is rather naive to assume that one bit of hardware and software will be the future of all personal computing technology. One size never fits all, I didn't really like my iPad, and as meaningless and anecdotal you may think my opinion is, there will be many people out there who either have no need or want something different from an iPad.
The fact that the Kindle Fire has sold well but not made a dent in iPad sales demonstrates this. More choice brings in more consumers. When Windows 8 tablets arrive, we will see more people buy into Tablets. Maybe even more if Google actually make a decent tablet version of Android. That doesn't necessarily mean that the iPad will fail, the market will expand due to there being more choice for consumers.
I'm personally looking forward to Windows 8. But hey, my opinion, and anyone else's who doesn't fit in with a pro-Apple mindset is totally anecdotal. Right?