I've always seen instant perma-death as a bit of a problem since this is a game that relies on an internet connection which may go out through no fault of the player. At a certain moment, that could and will, lead to the collapse of characters.
If I happened to be in the water for some reason, not even in any real danger, and then get disconnected and drown, I would be understandably upset to find my character perma-dead upon finally being able to log back in.
So I am all for the idea of being knocked out in the deep sea and floating with the tide to where ever it may take me, and more importantly, give another character the chance to rescue me.
Avoiding the simple walk-the-plank and fast travel issue, when a character falls unconscious, wouldn't it make sense to black out the screen during that time? I think ARK does something like this. There's not going to be a mini-map so there isn't a way to tell where you would be floating off to. When you woke up you'd have no reference for knowing where you are.
I am curious how spirit walking (or swimming) will work out in the water. Will you just spawn in the spirit world a certain distance from your body and have a counter start running down? Can you spirit walk with your body still floating on the water? When you catch up to it, will you be able to start swimming? As far as swimming mechanics go, will you have to actively move or tread water to avoid drowning?
So many questions...