This has been in the works for years, so telecoms have had plenty of time to get ready. They've also been offering much better roaming rates the past few years within Europe.
Brussels makes rules, but doesnt understand the market and industry.
Aren't those regulated by this as well? I remember the first EU data roaming regulations targeted only what the operators charged each other rather than what they charged the customers, so there's precedent at least.
Most of the telecoms won't be paying at all, except as an independent exercise; they're nearly all owned by one of about five companies (or else are MVNOs who are already accustomed to paying for data etc for their customers).