Ten replies so far, and no one has suggested the obvious: They don't want you knowing where you are on the list before you check in. If you "need" to be in a premium class, and knew you were at/near the top of the waitlist, would you pay for the seat instead? If you have no idea, you are more inclined to pay for it. It helps to sell F seats.

This is also proprietary info - if its open to you as a pax, its open to anyone, and I don't think UA would want their competitors looking at this data far in advance. This data, IMHO, will never be publicly available.