Actually, it would be exactly the same as some kind of (viral) Apache Licence: you can extend the protocol ONLY if your extension is open source too
It already worked (more or less) for software... why wouldn't it work for open protocol ? And it would avoid the "embrasse, extend, extinct" strategy used by Microsoft or Google to transform an open protocol into a closed proprietary using extension and the size of their user base...
I am not sure open source licenses would help, because the value of various platform came more from the data that they run with, and not so much the code. Especially with the increase use of AI, where there is a lot of value in the models, and those are not necessarily subject to redistribution clauses of open source licenses.
And if there were a license that says "you must also share all your data", it would imply compliant services can not hold private data, which makes it undesirable to companies and users alike.
Because it doesn't really make any sense. I can make my software compatible with yours completely against your will, and I can extend my software as I wish.
It already worked (more or less) for software... why wouldn't it work for open protocol ? And it would avoid the "embrasse, extend, extinct" strategy used by Microsoft or Google to transform an open protocol into a closed proprietary using extension and the size of their user base...