Hello, We'll certainly consider that as a new feature. For the moment, adding the following code to your form may accomplish what you want (in the custom code section of the form builder):
This should swap all of your textareas to TinyMCE edit boxes, allowing for html rich pasting. You may want to increase the height of your textareas in the FormBuilder interface, under Advanced:Number of Lines, just to be able to give your users some room to maneuver.
I don't think this will be a perfect solution, so please let us know what problems you run into, so we can see what might need to go into a 'rich text input' feature.