Well it's a bit of a hacky fix to be honest. What it does is allows players flying an elytra through the server's built-in anti-cheat, meaning it doesn't spam them from moving too quickly and doesn't lag them out either. Haven't been able to test with boats; do they even travel that fast anymore?
Yes, that gamerule fixes this issue!
Still present in 16W06A
Confirmed for 16w05b
I think this bug needs writing that it not only spams the log, but also rubber bands the player like this: http://i.imgur.com/C5Viayn.gifv
Currently what's written about the bug doesn't hint towards this at all, making it look like just a 'console text spam' bug.
Still occurring in Snapshot 16w02a
Here's what it looks like: http://i.imgur.com/C5Viayn.gifv
Breaking for cool maps 😞
Still in 1.9-pre1