1. My larger point is that this license simply is not going to interest a lot of people because they don't have patents to begin with. Only a minority of contributors will have patent claims, and almost all of them will be commercial contributors. They will simply not be interested in such a license and not contribute to a project using it; for people who don't have patents, the additional patent grant does not make a difference, other than that they're possibly scaring away contributors who do have patents.
2. The point here is that the license may require you to grant rights that you can't grant, ergo you can't contribute work under the license. The license requires you to grant any rights that you hold, but you may not have the right to grant such a sublicense. The Apache license, in contrast, only requires you to grant a license for patent claims that you can actually license.
3. My point here is that the patent grant may be uncomfortably broad especially for commercial contributors in that they give up rights that they're not willing to give up.
4. This is quite different from the Facebook situation. It's one thing to allow others to use your patents; patent holders may be much more reluctant to unilaterally disarm defensively, too. In order to get them to accept such a broad patent grant, you have to convince them that this in their best interest, too. That you can convince people without patents to their name to use the license is irrelevant, as it does not matter whether they use a license with or without a patent grant. If I were a patent holder, why would I give up my defensive rights against third parties along with a patent grant for using the software? How would that serve my interests?
5. So, what are the usage rights if you believe that this is a well-defined legal term? Can you be more specific? How are they related to patent claims? Have you researched whether this would include sublicensing rights and whether sublicensing scenarios need to be considered separately?