It's sad that Veeam can't be more flexible regarding licensing. I understand that mixing licenses would give customers the ability to use higher features for all of their VMs and I don't know how you could prevent that.
On the other hand there are many features which are just necessary for a single VM, host or cluster.
For example Exchange or Oracle; most customers have just one of those Applications in a single VM and don't need anything else from the Enterprise Edition, but still they are forced to go with the expensive license.
A smaller two host test cluster, where Standard would fit, is not possible if you have a higher Edition for the main cluster in use.
Perhaps it would be best to license each feature one by one; increasing the license price by 50$/per feature.