It would be nice to get a validation tool if the trader is an active tax payer in EU System - VIES or National Tax portal (Poland).
Such functionality would need to:
validate in government/EU tool if the supplier is an active tax payer (for one selected or group)
Check or validate before/after posting if the Vendor/Customer is a active tax payer (receive goods, deliver goods, post invoice)
Store the history of checking (in case of tax control) – by adding the screen shoot from tax/ EU portal for a specific date.
Create a report which could validate if existing documents (invoices) for specific vendor are OK (status of suppliers is Active)

This would be a good enhancement in the system, even there are available add-ins on market prepared by third parties.