I don't know how good the success rate is on being waitlisted and eventually getting moved up to F are, but for me, it's been 100% positive. Once I called to get on a later flight that had F saver available and was told I'd have to pay a fee to change flights. I declined as it was Lax/Sea, not worth it to me.
A few hours later, I got an email from Alaska saying I was moved to F on the original flight. Not sure if it was coincidence or just a nice agent.