We recently added the ability to send an email using the new email technologies directly from an opportunity card, similar to how you can send email from a contact - reusing code where possible. However, we also extended to have a default word template signature that was populated based on the salesperson.

Whilst we would love to do a pull request on the actual baseapp, we aren't a partner - just an advanced customer. However, we also noticed that there is no ability to extend the behaviour of the standard sendemail action on a contact card.

We would love the ability to have an OnBeforeSendEmail integration event that allows us to interact with the TempEmail item in a way that we can extend the behaviour. Of course, others might like to include the ability to send email from an Opportunity (including a link to the opportunity record itself as well as the contact) and see prior emails.