It's conceptually viable; it's just not materially viable yet.

In all seriousness, I seem to remember that there was a practice of testing for viability using very similar means – basically, are people interested enough to click through, then collect emails.

So perhaps this is a path to demonstrate viability by questionnaire.

An MVP should consist of the minimum work required to test an hypothesis. In this case the hypothesis is: "People would buy a browser if it offers an ad-free experience". So it's viable according to that idea. Viable doesn't mean useful though :)