Funny, I have been thinking along the same lines.
While I would love to do a three gun match, I think it is a little over the top for me. I was thinking of talking to the local IDPA match director tomorrow about incorporating a rifle or a shotgun into a stage or two over the year. this would of course be a bonus stage and would not be scored. I know there are other clubs that do this, with BUGs as well. It would be nice to get used to shooting a pistol with a slung rifle or shotgun, then transitioning to the long gun. This could also be done in the opposite order.