My thinking on how replies should work with respect to edits, without knowing how it actually works...

The edit should point to the original message. Clients should render the edited version if they know about it. But a reply should always refer to original id - even if they never saw the original version.

That way threads stay sane for everyone involved, including for clients that don't understand replacements.

Furthermore replacements should not be kind 1, otherwise they look like duplicates to clients that support replacements.

To avoid ambiguity about what you actually responded to, a reply could *also* point to the edited version in a separate tag.