These are some really fun ideas. The 1x/2x/3x speed controls are probably the first thing I’d like to experiment with, and a streak achievement for playing at 3x would fit nicely.
I also like the distinction between a resumable Endless Mode and a one-run Endurance Mode. They would need quite a bit of balancing, but they could add a real late-game challenge.
The Kraken event fits the game surprisingly well too, especially during a Moonless Night. And using the sirens’ song against Cthulhu is a very clever idea! Sharks could work as well, as long as the player gets a warning and a chance to protect the boats.
I can’t promise all of these yet, but I’m definitely keeping them for future updates. Thanks for taking the time to write such detailed suggestions!