Hi,
This would be a very useful and quite simple feature.
Simple feature ?
I'm afraid that you do not see the complexity and the development time that this "simple" feature would require.
You are talking about modifying the order system core and all views depending to an order (front-end customer order, back-end order, order edition, all order emails, add-on views, etc) ; and by the way change completely how the "order status" is working.
And if you want a "partial ship" you (or someone else) will also want a "partial refund"... So I'll need some antidepressants.
Regards,