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To put it in perspective:
The actual status button can have 2 circular arrows and a text called Sync, acting as a button if there is unsaved data on the page.
That is the most we can do with keeping a solution sane from a performance point of view and also storing cached information in the factbox area.
Further solutions for instant save:
If a user really wants something instantly saved, a Sync button can be added that would sync these changes to the database. More of a push rather than a default change after each field.
However the power with this factbox is that the data would be stored in a different adjacent datastore and act as a cache that ensures no-one loses any work, together with the Sync button it would provide an instant save if really needed (if a user wants to block a customer/vendor/item and take effect immediately).