Sure, but that's essentially a weaker recovery password (which also is an option in Proton).
Also that poses quite some challenges for email verification (say, you make a typo when you first write your address), let alone the fact that you won't see what emails you have configured essentially, which is also bad UX.
I think it's much simpler to have recovery email as it is and -if one doesn't want to associate proton account with any other account- offer other recovery methods, which are available (phrase and phone number).