I'd like the ability to create a lookup field on the 'Customer' entity, similar to that used for a Case. This would provide support for a number of scenarios where the primary, or even secondary, record could either be a contact or an account.
We released this as part of Dynamics CRM 2016 Update 1. (v8.1)
Please refer to the following link for more information:
https://technet.microsoft.com/en-us/library/dn531187.aspx#Types of fields