This new patch content is arriving tomorrow (20th March) in the EU with the usual class tweaks and a variety of little changes to various trinkets, etc. More information on those can be found here.
The big news for this patch, however, is a new "outside of WoW" limited time game called Plunderstorm. This will (apparently) be selectable as a new version of WoW. It is available for anyone with a WoW subscription - so if you're currently only playing classic and don't have Dragonflight, that's fine, you can still play.
Playing gives the opportunity to gained various cosmetics, pets and mounts for your actual WoW and Classic games.
It isn't based on your current WoW characters but gives you a selection of preprepared characters to pick from which, as you play, gain in abilities and upgrades. As an added bonus, for those of us who are a bit rubbish at this type of thing, you don't even have to be alive to gain rewards! Woohoo!
Blizzard states:
"Get swept away in the Plunderstorm — a fun, new, limited-time, pirate-themed event of prodigious proportions lasting the next several weeks. Scour the map and try to be the last pirate standing while dashing across the Arathi Highlands to find abilities and upgrades while plundering loot just to survive! Players can earn cosmetics, pets, titles, and mounts as they progress through the reward track, including a majestic Plunderlord parrot mount, Bubbles the crab pet, swashbuckling cosmetics, and more. A victory is not required to claim the spoils of a well-fought fight."
For more information see their page: https://worldofwarcraft.blizzard.com/en-gb/news/24073142/shiver-me-timbers-make-ready-for-the-incoming-plunderstorm
They've also put out a couple of videos:
