Bill's been talking a lot about whether the IDE offers incompatible libraries and examples. But I can't find any mention of that actually being an intended goal. If the metadata is going to be used to filter what libraries, examples and other options are offered to users, I can't find anything written about how that's supposed to work.
The spec does talk about 2 goals: #1: facilitating a library manager that automatically downloads libraries from a central server, and #2: supporting multiple architectures.
Regarding multi-arch support, I must agree with Bill, requiring a directory structure that isn't compatible with 1.0.X is obviously going to lead to very slow adoption of this spec. As the author of several libraries and the current maintainer of several more, it's pretty easy to choose between publishing in a format that works on all widely used Arduino IDEs, versus a format that only works on the newest.
Cristian, I'm really glad you said this:
First I want to reassure you that if you want to stick to the 1.0 lib format, you can safely do that, we are not going to remove old library support. We already discussed that (in a google issue maybe? I can't remember), so I don't know why you're so concerned about that yet.
I'd like to point out some language near the end of the spec, which might be the source of concern:
At some point in the future, the IDE will drop pre-1.5 library support. There is no specific timeline for this, it will be determined once the new library format has become widespread.
Maybe this part of the spec should be updated, if you're really committed to keeping the old format supported?