I decided not to convert EnForward, which forwards messages to Evernote, for Thunderbird 78 (MailExtensions) once. However, because I've received some update requests, I reconsider the plan.
I've started to work to make EnForward compatible with Thunderbird 78. Its feasibility was confirmed and core code was migrated into MailExtensions. I think the first beta will be available in a couple of week.
[2020/8/3]
EnForward 2.0.0 is released.