The nice thing about the "Hubspot User" type of field is it acts like an automatic dropdown and even shows you the persons email when picking the user. What I am proposing however is that you are able to email directly like you can with a text field that has an email in it. This should be easily possible since the email is already assocaited with the Hubspot User. Additionally it would be nice if there was another type of button like the email one that you could click and it would either take you to that Hubspot Users contact page or bring up a minature window. This would help when wanting to know their phone number to call.