Thank you for the request.
This iFrame Field suggestion will require a number of UI changes to dbFront, both for the Admin side and the Client side.
The iFrame dimensions and positioning will require some unique consideration. The CSS could be used for the fine-grain layout, with the choice of the container [FormTop, FormBottom, Inline, SideBarHelp] determining the primary layout.
NOTE: Please vote on this Feature Request if it interests you.