I want, that enigmail will be included into thunderbird. I have try to create a seperate package, But I have to realize, that you need thunderbird source to compile enigmail. So I think, it may be the better war to include enigmail into the thunderbird package.
I want this too, but unfortunately this is impossible and unsupportable. A separate add-on package is the only way. And yes, this means having the source in two places. Unavoidable.
Submitted for review, see Bug #239336