Currently, it seems that the new proposals and estimates feature only allows ONE signer per document. Many, many contracts have more than one signer to them. For instance many marketing agency service agreements have a representative of the agency as well as the client sign them.
Many proposals need to be able to allow multiple people to sign. Give the ability to attached multiple contacts to the proposal, choose which person needs to sign where, and the ability to assign a Team member as a signer as well.
I use sign.zoho.com for digital signatures. It lets me pass the document from one person to the next, and can collect multiple signatures on a single document. I'd love to see this feature added to Estimates & Proposals.