Some of your suggestion are already implemented or planned for the upcoming Steam Edition of Raft coming to Early Access sometimes this year:
* There will be multiplayer coop
* Eels as new enemy protecting underwater reefs
* Underwater exploration is in
* You can now sail your base raft
* There will be islands though they'll be small in size.
* Seagulls are in and will eat your crops if you're not careful. You can keep them at bay with scarecrow but Seagulls will eventually tear it apart.
* iirc furnace is in (for smelting metal), and there will be research station and with it research. There are changes to existing stations as well.
* There is a new resource: plastic and there are number of new fishes to fish and new crops and trees to plant.
* Number of new tools will be available (makeshift binoculars and oxygen tank) and you can make better ones given materials and research.
* Game will have three game modes: Creative, Normal and Hard
* Plenty of new things to build and decorate your raft with including upgrade options for some.
And plenty more. Check out the development blog and Steam page for further information. Also do note that there is not going to be any further updates to free Itch.io version of Raft (it'll remain as free prototype/demo). All future development will be done on the Steam version.