Thank for your answer, in fact I already sign on the missing item, but imagine it come back in stock tomorrow, then I have two item that were in stock, but now, no more. That means that I need to wait again, and nothing is done to prevent this hapening again and again.
Now a real example, I wanted to order raspberry pi Clobber breakout, 128x32 i2c oled display and 4-channel I2C-safe Bi-directional Logic Level Converter. I put in my cart the clobber and the level converter (it was in stock) and put the oled display in my wishlist. Then I subcribed to be notified when the oled will be in stock.
But the problem is that now the level converter and the clobber are back ordered. So if the oled come back in stock I can not place my order and nothing prevent things to happen again. The idea could be that we can order items not in stock so this kind of orders take all item of the order in stock to be reserved for that order until the missing item come back in stock. It is just a idea. But for now I placed my order of all item in stock because I do not want them back ordered again. The drawback is that I will pay both internationnal shipping (in the best case of my 3 missing items will be in stock at the same time, which is not sure)