Price? We know the price at least roughly. Surface with Windows RT, same price as a similar spec iPad. Surface Pro with Windows 8, same price as a similar spec ultrabook. Personally, I think you can take that to the bank.

App Pricing & Availability - this is only an issue for Metro apps, so this is only a concern for Windows RT and Surface. Windows 8 and Surface Pro run all of your Windows applications and you know how much they cost. I have yet to find any Windows application that does not run on Windows 8. So, this also removes any questions about compatibility with legacy applications. If it runs on Win7 it will run on Win8.

That only leaves us with one question, battery life, and I agree that is a question mark, and a big one. To have a real shot at the iPad, I think that Surface with Windows RT has to match the iPad's battery life. Surface Pro may not need to match it, but it will have to put in a pretty good day's work without a recharge, say 6 hours minimum. I'd look at the ultrabooks for comparison, and I haven't looked at their real battery life.