I did what you are proposing once for a transcon; it was a gamble that I won, but not until at the gate just befoore boarding, and I ended up with a window seat vs. the aisle I had before (at least the window was a bulkhead). In the end as I was sweating it out at the airport after the 24 hour and three hour EUA's didn't come through, I realized that I would have been better off just leaving the upgrade request in place. But, if it's totally open and you could put those 15,000 miles to better use than a domestic upgrade (as I did after I removed myself from the waitlist), you might want to roll the dice. I guess the point is that if you remove the request, even if there are seats available, you may find yourself sweating it out at the gate.