Excellent review. I'd nominate this for notable since it's important to figure out. I think we've moved on because we thought we did have it, but did we?
Here's what stood out to me when reading your analysis.
> Apply the keystone
So whatever it is, it's a tool (physical or informational) that can be applied to something. Q says paint the picture. So the keystone is a paint brush.
Say we do have it. That USI+POTUS+NSA is the key, and patriots are the stone… How do you apply that? I don't recall seeing someone try.
Perhaps it just means that we're supposed to take the information and become the force pushing it out to the public? I don't think so. Sounds too simple. No reason Q would have to be so cryptic about that. No reason Q would get annoyed that we still haven't figured it out yet.
How do you apply the keystone?