With multiple servers added into WHMCS it would be a great feature to be able to select at the product level which server to automatically provision to and not just whatever is selected as the default server in the server list. This will allow shared hosting companies to put reseller packages on one server and shared hosting on another, or "big accounts" on one server and "small" on another. This also could allow a company to sell "raided hosting" on a server with raid and non-raid hosting on a server with non-raid and have it all automatic. We will primarily use this feature to automatically setup stuff in multiple datacenters using one WHMCS instance and user selectable for provision.
This is already applicable by usage of Server Groups, and specifying which group under the Module Settings tab for each product. Simply create multiple groups depending on the server specifications, and assign them to products.