It's not MVP it's a Kite [0]. Minimum Viable Product is an actual "thing you can use", not mere concept. It's more than a prototype. The term implies it's something you can actually ship to customers.
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 :)
[0] https://en.wikipedia.org/wiki/Trial_balloon