Guess I'll have a go at some of these, caveat I am very much an amateur/hobbyist .
I want to do gliding over big chunks of terrain, probably needs dynamic world grid loading/unloading for memory purposes
Absolutely can, but yes to grid loading, for example (not actually watched, but probably relevant):
Dunno if the video covers it but REALLY big worlds you will want to keep the player stationery and have the player controller move the world relative to the player. Can't remember where I read it, but I think if you don't you will start hitting float precision issues when the character goes too far at some point.
My own dabbling with large-ish worlds (3kmX3km) was just static terrain with a LOD system and there was no issue. Will need to code the system yourself till 4.0 drops, but again plenty of tutorials/addons that explain or help.
I want to generate a plane of polygons in realtime, based on the normals of the terrain
I've not done anything like this myself but suspect this would be a good place to start: https://docs.godotengine.org/en/3.2/tutorials/content/procedural_geometry/index.html
I want to generate 'ramps' on the terrain, imagine shooting an ocean wave from the player freezing it and then jumping off of it
Hmm, I can only imagine this being costly at runtime, but fairly sure you could generate a CollisionShape and pass the 'wave' mesh that you generated to it using set_shape(). Then again if you're generating a wave programmatically (well beyond me lol), you can generate a simplified/primitive based 'ramp' shape that is equivalent and use that. Probably the same in other engines, but non-primitive CollisionShapes are no fun for performance.
finally - can Godot handle large animated creatures, like think shadow of the colossus as the best possible comparison I can draw?
Can't think why it wouldn't, honestly not tested this. Again I presume performance 'could' be an issue depending on the complexity of the model, as I don't think culling will place nice but again, not something I've played with myself .
does Godot do non photoreal rendering/shading well?
There's a built-in Toon shader as well as plenty of variants/tutorials people have made for this if that's what you're after. How 'well' it does it is up to you really, I don't have the experience to say if it does anything better or worse than something else, but there are some good examples of what other indie devs have made here:
