I thought the same as what Lyman said. Seems like it is possible to ensure that the distance is not short and I think that's the main criterion.
On the other hand I can see the sense in what Gene is saying. In most cases it's probably not a great idea (i.e. not worth the extreme effort to document and monitor).
It's an interesting conversation. Personally I don't think we need to make one universal decision. There may be room for some to go ahead and certify XC courses with adequate specifics, then we can try to assess that effort once there's a little experience with it.