Great post, Marguerite!
I agree with your three wishes and hope they are granted.
My own wish is that it would be useful if the P4D results were comparable to the PISA results. This would imply slightly altering your wish #1 to include link items in P4D that are also tested in PISA. The way I see it, this would avoid creating perverse incentives for countries to take P4D so as not to be compared with other countries. I believe that comparisons between countries are partly why PISA is so useful. My understanding is that this is what the OECD already plans to do, so my wish is also on the way of being granted.
PS: Posting to this blog was a bit of a hassle. When I tried to do so, I saw multiple copies of your blog entry with a "verification" field somewhere in between these copies.