But here in Poland the government apparently found a solution to this problem - it's called KSeF and it will force all local entities to send invoices as XML through their portal first (there will be no other legal way to invoice, because the KSeF number which is generated by the portal, is required for every legal invoice, without they won't be able to deduct VAT).
Only time will tell if this will bring new era of electronic invoicing or just another failed government project.
As for whether or not it will work, I think as long as Polish companies need to invoice non-Polish companies and vice-versa, trying to standardize in this manner will be challenging.
Do you know of a QuickBooks-scale accounting system that does EDI easily?