If there would be “ideal”, “light”, “perfectly developed” and “one fits all” kind of plugin, world would be wonderful 🙂 and I would call you “my Master” 🙂
Unfortunately, reality is as it is, so I fully understand your position. You can’t cover every need.
Nevertheless, your addon to xstore is already good. Now it is just a matter of “proper” logic in estimated delivery calculation.
For now, you can skip “pre-order” part and “custom non working dates”. This will cover most probably 90% of users’ needs 🙂
Other laggards – like me 🙂 – will manage differently with “non-standard”