Let's say you want to mix platforms, nodes or a sub-components in your cluster, what are the restrictions? 

There are multiple components that you could mix, we took everything into consideration and explained it’s compatibility.

In our portal, you can find the Hardware, OS, Storage, Encryption, DIMM, Hypervisor and vSphere restrictions. check out our Compatibility Matrix.

For example, if you want to mix the hardware you can mix nodes that use different CPU families in the same cluster, but not in the same block. 
e.g, a cluster can contain nodes from any NX generation, but a G6 block must contain only G6 nodes, a G7 block must contain only G7 nodes, and so on.

For AOS, all the Controller VMs (CVMs) in a cluster must use the same version of AOS.

Note: do not configure a cluster that violates any of the rules as it could lead to an unexpected behavior. 

For the full documentation and rules check out this: https://support-portal.nutanix.com/#/page/docs/details?targetId=Hardware-Admin-Ref-AOS-v5_16:har-product-mixing-restrictions-r.html