Blizzard has cleared the air regarding mythic raid mounts drop rates during the World of Warcraft Shadowlands pre-patch.
They posted on their forums earlier with some additional details to clear up the confusion, writing,
“The drop rates of the mythic raid boss mounts won’t be reduced until Shadowlands so there’s still time to collect them.
Feel free to refer to the Time Runs Short article for all the details of what’s going away and what’s going to be more difficult to obtain in the pre-expansion patch and Shadowlands.”
It should be noted that your ability to earn Ahead of the Curve: N'Zoth the Corruptor and Cutting Edge: N'Zoth the Corruptor will be removed during the pre-patch. If you’re curious about the pre-patch, here’s what’s changing. And in case you missed it, Shadowlands was delayed out of October with release planned for sometime later this year.