Would be great and more immersive I believe if we could do a bivvy anywhere, not only at designated spots. For rest I'd rather pick a place not known by anyone around. Beside it feels good to do bivvy in a place I've decided to pick during long walk if the plan is to move under the night only - not to change the route just to get to designated places for a few hours of rest. It seems non economical and not safe to do extra miles just to rest in designated place. Place other enemies/civilians may know.

There are those places like bushes, where player could camp for a few hours with minimum to none risk of detection. Other - more open - could bring a risk of detection, especially if patrols go around often. If detection happens because of bad decision about where to camp... Well... Next time player would be smarter.

I'll take an option of "camp anywhere" with open heart, even with no any animation. Just with option for how long to rest (wait for night, ect.).
Just simply animation of rolling out the sleeping bag and sitting down would be amazing. Available crafting and change tactic option would be great too.