it would be useful to be able to designate the type of field that results from a calculation to determine how this field behaves. In our case, we are using calculations with text to compose a URL that we want to be clickable. The URL custom field type allows this, but the calculated field does not. Designating (with limits) what type of field results from a calculation would be useful.
Alternately, letting custom fields be defined by type and their content to be defined by a calculation would be an alternate approach.