'Watching' for first messages only

Sounds like an implicit request for more frequent digest email options to me.

We don’t have any plans to work on this in the near future. If you’d like to purchase an enterprise hosting contract, we can consider adding it in some form, but I strongly oppose adding additional notification states beyond the four that we currently have (muted, normal, tracking, watching).

Otherwise you can sponsor the feature in the marketplace category here if you have budget for it.