Whales would be cool, but they would have to be in water only, making it useless to fight against.

Sea turtle= shellsnapper

Seagull sounds alright but it's have to do something new to differentiate it from the other flying machines.

The only difficult thing here is how to make it work in combat. Even monster hunter tried it and backed off from it on the next game, only keeping the leviathan type monsters and some fish ones that most people dislike. The Tideripper does have a leviathan type feel to it, the Leatherback turtle could work like a mix of tideripper and shellsnapper so you got that.

The Whale though... I think we could use something like the San Francisco underwater city and the fights in Deathstranding. We have buildings rising just a bit above water while the whale smashes against them, dropping us to the water and we have to climb up again. It should have tons of range weaponry, perhaps be able to surface and smash us and then retreat to the water again and, of course, jump above buildings like a rockbreaker. We could enhance the mobility of the character with the pullcaster and shieldwing, jumping from building to building.

So its possible, just a lot of work for just one machine perhaps... still I hope they do something similar. I really want a big whale to fight agains.

I think that the seagull machine could be in larger groups than other recon machines and could be a mix between the burrowers and skydrifter it could fly in the air and start scanning and do it in the water I think it could be more stronger like blasting purgewater and it could also be a midweight to justify it's large movepool and it would attack in groups like a clamber jaw.

A whale machine could be something like an underwater tallneck but also a mini cauldron for repairs and refueling of other machines.

Separate idea: maybe the whale is so big that it is where you can fight the machines that don't come ashore.

Overriding it gives you access to its defenses having a sort of naval battle with some machines and then Aloy goes over to solve puzzles to damage it further.

The whale could be like the Subnautica Leviathan- you know, the Ghost Whale.

Yeah a whale is too big to fight. It would be a communication class.