In reviewing this forum, I gather that development has stopped or stalled but I’ll post this here regardless.
It would be very useful to right click a message and initiate the creation of a rule based on the subject or sender of the message rather than the manual process of needing to copy that information before heading over to the Rules area in preferences.
In addition, the ability to export or sync settings in Mailspring between computers is sorely absent. I see that this is a recurring request, though. So +1 from me.