Given that there are 9 new cards, and there will be an update pack product, I'm assuming the update pack will contain an even 100 cards. Each non-Victory card requires 11 cards, and if there are 9 of those, that uses up 99 cards, for 1 blank. There's not room for a single new Victory card. Based on that, I am predicting Island won't be cut and remains the single alt VP card in the set.
As Seaside currently has enough blanks for one more non-Victory card, it's logical that 8 cards would be cut from the set.
Here are my predictions of what stays and what goes:
100% chance of staying:
Caravan
Fishing Village
Salvager
Warehouse
Bazaar
Tactician
Lighthouse
Ghost Ship
Ambassador
Outpost
Wharf
Smugglers
Haven
Probably staying:
Island (errata to not reference a mat)
Native Village (but what about the mat?)
Treasure Map
Take it or leave it:
Merchant Ship
Treasury (replaced with a Hireling for +$1?)
Probably leaving:
Navigator (art issue?)
Pearl Diver (art issue?)
Explorer
Cutpurse
100% chance of leaving:
Pirate Ship
Embargo
Sea Hag
Lookout
If Pearl Diver and Navigator both have to stay, then probably Merchant Ship and Treasury are gone instead. If Native Village has to go (which would be a big shame), then either Explorer or Cutpurse stays.
Regardless of what is cut, I can't wait to see the new cards! Seaside was my first expansion, and it was good times. The attacks are brutal, the swings are big, but that's all part of the charm. Despite the duds, there are quite a lot of unique concepts in this set. The new cards in Base and Intrigue added a lot of life to those sets, and I'm looking forward to breaking out Seaside again with some new cards.