I'm not entirely sure this is the correct place to make a suggestion for Userforms, but I know the people who develop it read here regularly.
I'll explain the (simplified) scenario first, which will hopefully make the request a bit clearer.
We have a form that has a common section, then splits into two parts based on a question about whether they want to contact department A or department B; both departments have fields they want to make mandatory for the user to fill in.
We have a form which hides department A requirements if department B is selected, however if there are required fields in the department A section, then the form will not submit.
So my first part of the suggestion is simple; in the 'validation' area, either make the option 'Is this field Required?' into 'Is this field Required when not hidden?', and only validate shown fields.
The next part is not required by me (yet), but I can see someone else may use this feature; allow the user to select an email based on a concept similar to 'Custom Rules' in the form; eg use when [field] is [value] [text] - as a real world example; radio_button1 is sales, radio_button2 is support - use "email@example.com when radio_button is value sales", "firstname.lastname@example.org when radio_button is value support", and be able to specify a 'default' email address for the form.
Hope that all makes sense!