As an aside, since RARE has most likely not even started making the video yet, here is an example of a way they could tell us a bit about what they are planning while still keeping to their policy of having lots of surprises in store.
Lets assume they have an update planned which will include the addition of a Megalodon Attack emergent event on the high seas, 2 new kinds of aggressive wildlife for islands, and a third ship to go alongside sloops and galleons. These could be announced in the following cryptic yet informative ways
"The Kraken will be getting a new friend." This would let us know that a new high seas monster battle was on the way, but still let players have that "OMG it's a giant shark!" moment the first time they see a huge dorsal fin breaking the waves. For all we know, it could be a new version of the Kraken that behaves very differently, or a giant crab, or whatever else.
"Islands will be getting more crowded, and more dangerous." Again, this would reveal that new somethings would be waiting for us on shore, but not clarify if they were animals, new skeletons, NPC pirates looking for a fight, etc.
"The ships that sail the Sea of Thieves will be getting more interesting." Which could mean new ship customization, new ship types, new features aboard existing ships, and so on.
Hope this in some small way helps RARE decide exactly what to say in their videos, the next one and beyond.