I appreciate that there is and should be a different levels of engagement, and I'm glad that it's easy to mark people as 'prospects' in Nationbuilder. However, it's very rare that I'd send something to 'prospects' that I wouldn't also send to 'supporters'. Please, let me do it in one step, instead of having to create the email a second time.
We will not be supporting sending the same email blast to both. Prospects have not opted in for communications from you, that is why you have to send them separately. In politics, it is technically possible that they have opted in for voting communications via email through their voter registration, which is why it's not illegal for you to send them email, and is why we have this option to end email to prospects. But the spam profile on them is significantly different, and it's important to keep them separate.