As another datapoint, I agree with @tobiaseigen.
I am admin of a wordpress site with several thousand fairly active users. We are about to migrate from using the standard WP comment engine to using Discourse. In the end, we’re confident that Discourse is going to be a vastly better discussion platform than WP comments, but the transition is certainly going to be disruptive and confusing to people who are used to what they are used to.
We are going to use WP as the SSO provider so that our existing users do not have to create a separate account in Discourse. For our purposes, to smooth the transition for our existing users, it would be a giant plus to have an option that is something like “Always send welcome message by email on new account creation.”
That might not be best for everyone, but we think it would be best for us and it seems like there are others with the same use-case argument. How hard would it be to implement that option and behavior?