License Validation should occur before Import containing data source
When someone selects Add option (accidentally) then as preventive measure application code should be intelligent enough to check for license eligibility and prevent user from performing the operation, what happening now is you are letting user perform an action which can potentially breach the license and brings down the whole system.
Consider the similar scenario but from different angle. With the same license if you try to add data source in Administration -- > Data Sources , You click on add button it will wont let you and shows appropriate message. But if we do the same thing from import export wizard then it allows you to complete the operation and post completion user comes to know that license is breached, Which doesn't seems right to us