I think an open source online commenting system, maybe like Commento, is worth offering as a service. Consider a commenting system that supports login-with-Facebook, Gmail, GitHub etcetera, spam protection, and email notifications (which I think most people leaving comments online want). Then, anyone who self hosts that open-source software, would need to do this, to get the same functionality as the hosted version:
- Sign up for e.g. a Digital Ocean Virtual Private Server
- Sign up for Akismet spam protection
- Sign up for some send-emails service
- Login to Gmail, read Google's tech doc about OpenAuth, and create OpenAuth credentials.
- Login to Facebook, read tech docs, create OpenAuth credentials.
- Github: read docs, create credentials.
- Forever onward, upgrade the server and software, to avoid security breaches.
This easily takes a whole day, because one will likely want to evaluate and compare different VPS and email providers, and also Google's and Facebook's OpenAuth documentation is not so easy to understand (I think). And a VPS + email service, is going to cost about $20 per month. ...
I imagine that for 99.5% of all people, buying a hosted service will be cheaper & save many days of work. Only somewhat large companies will want to self host?
(I'm building something similar to you b.t.w., https://www.effectivediscussions.org/blog-comments )