If waterwalk autopathing works as well as ship autopathing tends to do every now and then, u are still faster just using roads :^)

But jokes aside, with some tweaking this could be pretty cool

Jfyi - for ship autopath - I noticed that if u 1st stand completely still with your ship, board the steering wheel, then set the path and only after all this ritual u press T, then it won't lose waypoints, even with auto-breezy sail on.

If u do anything else, 100% chance for your ship to lose autopath on very 1st breezy sail (or do random 360' in the middle of ocean) xD

That's exactly how I do it as well.  Never get stuck on anything doing it that way.

Yes, I'm familiar with this and use it too. Just cracking jokes :)

Still less buggy than Dine trying to climb up tall waterfalls

Diné is useful during the compass grind since youll be in the desert a lot, during the padix piece grind since it's the easiest way to get to that island and a bit if you do the sailies, or even barter, because personally i use it to get to illya island  (using the map is faster but i need it for other things).

Other than that though, yeah it's not very useful.

To add auto path for water, first, they need remove stamina consumption on the water, otherwise it makes no sense, you will stop and fall in the water and you cant wait and back on  your dine.

As stated in the OP, stamina drain could simply be halted or made to recharge when on rivers.

Water stamina has been something PA has time and time again reinforced they are not removing. To try and assert a feature needs it or the feature won't be added would be to deny the feature entirely.

So for water autopathing to work, we could make it so that there is a depth check or a width check to ensure there is land nearby or the horse isn't on a surface that is ocean deep. In that case, the water stamina would recharge.

I like it. Great idea!