I checked this unlagged idea originally a week or so ago when it was first posted here, and was originally very impressed... however I don't think it's a viable choice for wfa.
Mainly because of wfa's preponderance of movement/push over damage. While it's great for dm'rs to be able to get credit for their aim and such, the push effect makes this unviable for wfa. Since, say a 300 ping sniper rails you slightly before you'd touch the flag, just about when you are landing on the flag, the server would send you the info that you were actually hit about a second ago, and you'd find yourself running into a corner, and by the time you figured out where you were, you'd be quite dead.
Most people are used to leading their rail/mega fire... not only would it create balance issues, but the above buggy effect would be quite hated... in wfa movement is all, and damage is secondary.