But seriously, there's zero incentive for the folks building these clients to make them interoperable. In fact there may even be disincentive, since the more folks they have on their platform, the more valuable the platform is.
Bringing it back to the topic on hand, this is very much an area I wouldn't want to see a heavy handed EU legislate something that just further cements the incumbants and makes everything worse forever... just like mandatory micro-USB would have been. I can totally see the EU legislating something like a mandatory Meta communication protocol with compulsory attestation from Meta servers.
Which is good, because the Lightning connector has DRM in the fucking cable, and gave Apple outsized and undeserved control over iPhone accessories.