I am also a bit confused as to why this is not already a feature? I’ve been forced to use the API and develop my own web form. If I can pull off this feature on my own with relative ease and minimal hours, I don’t see how Hubspot developers can’t add it?
I can see the potential difficulties in linking the contact and deal, and what happens with updates and duplicates, etc. but i would think you could put in basic funtionality with strict controls to at least make it available.