I think this is an interesting idea and will have a play around with
it, but will present an alternative first:
To see what happens when you change a particular field you can use
scenario outlines and steps with table arguments, or even simpler by
using the feature background to fill in the form, then in your
particular scenarios change the fields you want to exercise for that
test.
I haven't come across forms where this was not viable. If there are
such forms it may be worth wondering whether they are the best way for
a user to present data to the site, as they may be quite unpleasant to
fill in.
A problem may present itself in virtual attributes - some are written
and not read; this would be worked around by using machinist's plan
functionality (for controller testing). I don't know how it would
apply to factory_girl.
Another problem may be when you start to introduce selection boxes,
tickboxes, and the like. I don't think you can tell from the
attributes how the user interacts with the view to provide them. If
you take this away, then you're really talking about something better
suited to RSpec than Cucumber in my opinion, namely model specs.
Hope that helps
Nick