Ringo's "Armored Combat Suit" / Oneill family saga would be great (except Cally's War, it's just not that good). I want to seee them "maraching" into battle with the Immigrants Song playing on their sound systems. Folks will forget aboug Copolas Ride of the Valkyrie in Apocalypse Now!
The "March To" series by Flint and Weber including the new one, We Few, would make a great long form series, ala Babylon 5, though how you could sustain the nasty environment of Marduke would be a challenge.
Flint's 1632 univerese could also make for a very strong long form series. Might teach some people some history at the same time.
In the classics I've got to go along with Footfall (I want to see the Archangel Michael take off!!!) and Lucifer's Hammer would both be perfect for long form mini-series. Both would need to be updated, particularly Lucifer's Hammer, for science developments and some PC cleanup.
Definitely, John Ringo's entire Posleen war series would be fantastic on the big screen.