Horrible idea. Really what the regulation states is that iMessage must be interoperable with other chat apps.

In order words, if it wants to improve its service, it will need to get buy in from a committee of its competitors.

This is a solution in search of a problem. Consumers today can choose from iMessage, Telegram, WhatsApp, Slack, Google Chat. There's competition, and there's so many great options for each person. This regulation can only make things worse.