I don't see that ever happening under Vail's ownership. Pretty sure there'd be takings issues if the Forest Service tried to condition Vail's permit on allowing non-paying public access through private land. And the Forest Service would have to want to do it too. I've seen some appetite on their part to push lessees of public land to allow public access to that land (the reply Shralph received from ENF personnel was encouraging, and I've had similar conversations with FS personnel)--but there's a pretty significant difference between that and what you just suggested.
And forget about any kind of prescriptive easement/historical use argument. The elements aren't there.
ETA: I'm not trying to pour cold water on the idea per se. I think it'd be sweet. But I just don't think it's realistic without Kirkwood being owned by like a land trust or b corporation or something.