I really like the idea of life time purchases rather than subscriptions.
To minimize the risk that your site goes down (or is economically unstable at some point in time), you could consider making this a paid downloadable app.
I'd pay double for a self-hosted version, that isn't phone-home dependent.
This removes a huge risk that the service will one day disappear. (If your sites go down you may not be able to release a self-hosted version)
To minimize the risk that your site goes down (or is economically unstable at some point in time), you could consider making this a paid downloadable app.