Does anyone know of any actual *live* implementations of WebSub (or PubSubHubbub, any version) that use the .host-meta method of advertising the hub URL, or any consumers that check for it? I did a bit of looking around at some of the major players and couldn't find any that did. If you know of a publisher or consumer that supports it, please share the URL to it.
To clarify, I'm talking about the third method of Discovery listed here: https://www.w3.org/TR/websub/#discovery
publishers may also use the Host-Meta Well-Known URI [RFC6415] /.well-known/host-meta to include the <Link> element with rel="hub"
We plan to exit CR on 2017-05-11, and if we don't have at least two claims of implementations of that feature, we'll be dropping it from the spec when we exit CR. It's important that if any implementations of this feature exist, we hear about them ASAP.
I did add support to websub.rocks for discovering the hub URL using this method, and the test suite is now logging whether anyone publishes a URL that advertises the hub that way, so we'll get a bit of data from that. However I don't want to waste the time writing tests to check whether subscribers support this, since there's no evidence of demand for the feature. I also don't want the presence of the test to cause new subscribers to have to do the extra work of checking the .host-meta file just to pass the test suite.
So far, all known WebSub/PubSubHubbub publishers support rel discovery through the HTTP Link or HTML/XML tags, so there was never any incentive for subscribers to check the .host-meta as well, so I strongly suspect there just aren't any subscribers that check for it.
Since this feature is already marked At Risk, the data is strongly pointing towards dropping it on the 11th.
If this feature is important to you, then please show evidence that it's been implemented in any form, and I would also highly encourage you to write a test for it in websub.rocks.