Only on HN does a kind soul already have a list being curated for the exact thing posted. Haha. I love it.
That's a good resource, thank you for compiling it and sharing it here. Do you happen to know if there's any that allows for one user to comment with service A, and another user to comment with service B?
With all the tools that I've gathered, I don't recall a single one that would support multiple providers. Sounds like a gap in the market ;) Enabling multiple comment providers shouldn't be a problem, e.g. by adding "Comment with X" and "Comment with Y" buttons that load the respective service. But displaying aggregated comments from both providers is a bigger challenge.
Yeah, aggregating seems technically challenging, but doable. But I wonder if ActivityPub or some other "open social" protocol would suffice. I'm torn between "support open protocols in particular" versus "support as many things as possible".