What if we made it a law that like services must interoperate without interop fees to the consumer? Like all payment systems must connect, it's up to them how they do it, but they must. Same with voice calling systems. The penalty for non-compliance being a revenue tax on proprietary services (that don't interop).
The goal would be to discourage Walled Gardens, and raise revenue to fund protocol research and proof of concept projects. What might be some of the unintended consequences?