I'd think an scenario should be out for at least an year before it can be done as a Volunteers Series. : ) People need time to stumble across it, and go through it themselves. The case with most scenarios - they're all years old. When a Volunteers series begins, it's a great oppertunity to reflect on a scenario - or - play it along side the Series author.
Perhaps in comming years, Apotheosis, Portal of Sigma, and of course WMaiD can be covered by Steve and / or / Mark.
Steve, I believe EMR would be interesting. I believe the Marathon engine simply can't render (convincingly, anyhow) outdoor environments. Thus, I've never had the stamina to make it though the scenario. Metallic corridors, not caveman huts, seem better suited for this engine.
Be that as it may, I'd find an story analysis for EMR interesting as each level is played through.
Regards,
-Blayne [ernie]