While I understand the rationale for the meme (I, too, was a Google Reader user), I think you will find that Google's ongoing support for Cloud APIs is robust. Any potential cloud platform customer has to decide if they want to depend on a service or control everything themselves; there are tradeoffs either way.
Cloud KMS doesn't implement an open standard (there aren't a number of good open standards in the space, KMIP is probably the only candidate I'm familiar with), but use of the current functionality shouldn't be very hard to port to some other API. (Although, given the dependency on keys, etc., this may not apply to moving any reposed data, that's fundamentally more challenging.)
[repeated disclaimer: I work on the product]
