Payment on updates?

I wonder if we should allow devs to set a `recommended-update-price` or something that defaults to `0`, but would be a way for a dev to re-prompt for payment for significant updates (i.e. a large feature addition or new major version release).

If we switched to this and most apps went with the default of zero, we could consider also prompting users for the individual update when they hit update-all.

The flipside of this is if devs just prompt for payment on every update or something, so I'm not sure how this would look. But filing it here to open discussion.