A few years ago, I remember the FAA saying that primary radar
would be eventually phased out at many enroute radar sites. AOPA
was opposed to this. A number of beacon only radar sites are in
place today, and they would become more prevalent.

In the wake of terrorism concerns, is this proposal dead?

That of course isn't the only advantage to maintaining primary
radar capability. I also recall that when Air Canada's 767
became a glider years ago that they were lucky because they were
in one of the few spots in Canada where primary radar was still
available.