In addition to contact forms, JotForm is used to create many other kinds of forms: Surveys, lead generation forms, Facebook forms, feedback buttons, application forms, PayPal forms. That's why we keep the default toolbox with generic fields and keep most commonly used fields on the Quick Tools toolbox. But, I am intrigued by your idea and we will definitely run some tests with it.
I assume its not people who read Hacker News (as most of them are just as likely to build forms from scratch).
If your market is marginally techy - but not programmers - then I think you are probably spot on in the current iteration. It is very customizable, and you can build exactly what you need.
If your market is non-techy types that only know how to copy/paste an embed tag, then you may need to test with some simplifications to the workflow. (See Wufoo, they are pretty good at this).
Sorry if my feedback comes off as harsh. This exact idea has been on my "idea list" for a long time, and am really excited to see someone executing it in a nice way.