There's nothing stopping the requirements from being "mint us a certificate according to these specs" and additionally "okay, now pin this certificate in your browser".
What prevents an NSL from compelling Google from minting a new certificate (they are a CA), providing the keys to the bad guys, and distributing that certificate in Chrome? NSLs have been used in the past to compel positive action (c.f. Lavabit), so I really don't see how you think there's any practical limit to their power.
My understanding is that there isn't a limit. If I am wrong about this, then kindly reply directly here so we can all learn instead of giving the "read up on" non-answer.
To my knowledge the exact details of the Lavabit case were never released, but from what has been released it's quite clear that the issue was regarding a warrant and a gag order, because the ensuing litigation wouldn't have been remotely applicable to an NSL (otherwise Lavabit's attorney would have won on a walk).
None of this is to say that I think NSLs should exist. In fact, I think they're a terrible idea. But the vast majority of discussions around them and similar topics is so grossly uninformed that it's impossible to take most people seriously on these subjects.
No substantial difference from the concept I'm complaining about.