Currently we still have the default sitting animation with the legs bent forwards. Perhaps things would make more sense with them still pointing downwards but also outward in each direction?

This is how Survivalcraft does it, for example:

Boats and minecarts would keep the original sitting pose. This mounted pose would be used for horses, donkeys, mules, llamas, camels and pigs. I'm not sure if it would look good on striders, though.

I'll have to give it a shot, I am pretty sure the legs will then clip through the horse because it is too wide.

That's what I was worried about for the strider. For horses it should be fine, some horses tend to be hairy anyway so their coat could easily be occluding much of the leg even in real life.

I'll have to test it, can't say yet if this works/fits the mod or not.

I'm not sure, maybe I can add it as an option? But for my liking the legs clip too hard through the saddle. It would require moving the player up a bit, but that has an entirely different can of worms. I'll make it an optional setting.