[dimal]

That does not sound like an MVP. Then it’s up to random chance that they create the right API format and then someone makes an app to use said API and doesn’t also use it to steal data from gullible people. You’ve multiplied the number of ways this can go wrong and reduced the chance that anyone would use it.

[jacobyoder]

You've increased the places where things can go wrong (in third party client apps) while not having any control over their quality. We'd hear "oh, IRS opened things up!", then deal with a dozen half-baked clients, and conclude "IRS sucks at something so simple!".

Agreed - public API first is the wrong place to start.