Fair point. I was under the assumption that subpoenaing certs at least for domestic entities was common place. I guess that barrier hasn't been crossed yet, or at least we assume so?
After some amount of poking around, I've found exactly one case where that happened (https://en.wikipedia.org/wiki/Lavabit in connection with Snowden).
Law enforcement might subpoena, say, search result records in connection with a specific crime (certain keywords + location + timeframe), but larger companies with the resources would absolutely have the ability and incentive to fight something as overly broad as requesting SSL keys.
