Vague. Early 2027 perhaps with a lot of luck, for a regime that will at best solve a very limited subset of issues.

I'm not holding my breath.

For some perspective, look at how something with a much smaller scope is being "revolutionised". I'm speaking of intra-EU dividend taxation, as regulated in EU directive 2025/50 ("FASTER"). A slightly less complicated dividend double taxation regime between EU member states. Applies to dividends on shares in public companies only. If the shares in question have not been traded within 5 days from the ex-dividend date. If the gross dividend is below 100k€. If the member state is not very small. From 2030. Using EU standardised forms. In some cases, resulting in direct reduction of the double taxation at source. In other cases, refund of excess double dividend tax within 60 days.

The clean solution would be to tax dividends in the tax residency member state of the receiving individual only. That would require a rather large leap of trust from very financialised EU member states like .ie, .lu or .nl. Perhaps possible with a long transition period and compensations. Only there's also bad faith state actors like .hu randomly torpedoing EU legislation to extract concessions. This discourages other member states from even trying to implement the clean solution.

Long way ahead still:

> Given its key importance for the EU's competitiveness, the Commission is calling on the European Parliament and the Council to reach an agreement on the EU Inc. proposal by the end of 2026.