Hi,
The main problem is that, several products could be in the same time in an order. Warehouse system could be useful to separate the products in order to have one shipping method per group.
Like I said, you can already use it but you won't have a cool graphic interface.
The main problem will stay : there could have several products of different type in one single order.
For this single order one email will be sent. So.. Which email would you want to send ?
You can customize the email, it is possible in HikaShop 2.2.1 like in HikaShop 2.2.2 (with the new templating system) but there are many question to solve before thinking about a development and I don't think we can provide you this kind of support in the forum. It is something more like a custom development.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.