Ultimately we need 100% customisable emails, but even if a part of the email was customisable, that would be so useful.
We desperately need a custom content area field added to the client order confirmation emails.
We have products that we have to request further information from the customer after they've purchased, and with a custom field this would be possible for us.
It would also be great for upselling or spreading a creative message at festive times etc.