Do you know why? What makes you think we won't end up at
"There's OneAPItoRuleThemAll, but nobody really cares or wants to use it anymore."
or even at
"There's OneAPItoRuleThemAll, but nobody really cares or wants to use it."
If you cannot answer that, I wouldn't bother working on something like this.
Also, who do you think will be interested in having a common protocol? I think the answer will be "those with little data of their own". Big players do not want you to build tools that work together with 'their' data (clear example: Twitter: open while small, but now closing down its API)