I think we have speculated about this in the past, but my opinion is that it would be a lot more than just a "software issue".
The Model S with Supercharging capability likely has newer generation cell technology that could be more amenable to quick charging. As far as I know, the existing Roadster ESS has no provision to allow external DC connection to hook to a 'supercharger'. There could be cooling issues. Of course they would need to test any such changes extensively, and I doubt that would make financial sense for them to provide it. Sure, conceptually it is a nice idea, but I think it is unlikely that they would go to the effort of re-engineering things for a small number of Roadsters that would be willing to spend money on such an upgrade.
With all that said, all we can really do is wait and see if they do something...
maybe they transplant the charging/supercharging system from Model S into the Roadster!
Is this doable?