I'd love to see cross country added to the winter games. Mirror the World Cross and have a long and short course, with team and individual medals.
I also think it'd be great to expand the marathon participation to 5 athletes per country and score the top three for teams. Or failing that, score the top two of three for a team award.
And lastly, I wish there was more road running. I'd love to see the half marathon, though I understand when others say it would just dilute the 10K and marathon. So failing that, how about an ultra?