Access to licenses for extensions in ArcMap and ArcCatalog was extremely easy for users for enterprise customers using license manager. You simple launched the extension from the Customize toolbar and the application would communicate with the licenses manager to check out a license (assuming one is available).
In ArcGIS Pro, the available extensions are defined at start up. This means if a users wishes to add Spatial Analyst capabilities they must shut down ArcGIS Pro before that functionality is activated. This architectural change is expected to negatively impact user experience at our company (where we have hundreds of users of Desktop).
Please reconsider the architecture to allow for more flexible license capture.