Hello Josse,

seems like the answer on your question is in this video -https://youtu.be/38MbxQV7zTg

Picker picks multiple orders at once via Batch picking. Then, on the packing or delivery zone, the picker scans any item from the cart, and the Ventor app (Odoo inventory) shows to which order the product belongs. So, your pickers can quickly pack and ship your orders with no mistakes.

There are some handy tricks offering a lot of possibilities already, for example these use case. Make sure to tick the option Manage advanced routes for your warehouse from Settings > Configuration > Warehouse. 

1. Configure the warehouse as Pick Pack Ship from Warehouse > Configuration > Warehouses. Select your warehouse and in Outgoing Shippings, tick the option Make packages into a dedicated location, then bring them to the output location for shipping (Pick + Pack + Ship).
2. You need to activate Technical features for your user. Then go to Warehouse > Configuration > Procurement Rules, find the Stock -> Packing Zone procurement rule. Add a fixed procurement group by changing the value in Propagation of Procurement Group to Fixed.  Create a new procurement group with Delivery Method Partial.  This will bundle the moves from Stock > Packing Zone in one big picking.  
3. In order to test, you should create several sales orders and you will see that the moves from stock > packing zone will gather in one big picking for which you can handle everything that is available at once.  From Stock > Pick you will have one assignment per SO.

This can be elaborated further as you can create different zones in the warehouse which have products with different routes. 

I tried this solution in 8.0 but I can't make it work... It looks strange to me that it's so difficult to manage the use case where you receive more than one order from a customer and wish to organize deliveries by customer (sending for example one product from order 1 and one product from order 2, then create a backorder or similar) instead of by order. This use case is the standard for all my clients...

I am also looking for a solution in Odoo 11.

If I set the procurement group to "fixed", then there is one big picking, that's right, but the delivery orders won't be grouped by customer. So if I have 3 SO from one customer, that leads to 3 delivery orders.

Any solution?

Thank you