This discovery method is inspired by the way Go does package name delegation. It is really trivial to do.
We have gotten feedback that people would prefer to use a well-known URL. At the time we started building appc the well-known URL stuff seemed to not be getting much traction but this has seemed to change over the last few months. See this issue: https://github.com/appc/spec/issues/160
Overall, I think this sort of delegation and naming is really important despite the shortcomings of particular methods. I hope that as the Open Containers Initiative proceeds that we are able to make this part of the standard. If email can do name delegation to hosting providers our server software certainly should too.
It's an excellent hack, but it also just feels so wrong, at least in some cases. Most users (of a URL) won't care about the tags, so why send them? Maybe User-Agent differentiation is an answer? Define a string which indicates the type of response that rkt is looking for?
Are there any examples of publicly standardized User-Agents?
At least it would allow one to take meta tags to specialized binaries out of their webpage markup. Well known URLs is a decent compromise, but potentially breaks existing applications and extends across all applications.
Why in the world would you pick this as a discovery mechanism.
This means that any took that wants to do appc discovery needs to know how to parse HTML.