I'd turn Secure and Slaughter into an open world PvP zone, personally... I mean, it's already dead, changing it would give it a new purpose at least...

Just change the objectives to FATEs, maybe throw in some NPCs to fluff numbers... So your Grand Company outpost is defended by NPCs, hopefully preventing spawn camping and giving us something to whack if nobody else is around... Have the other locations set up as FATEs; Either to take or defend, for example, the Allagan Markets. Then just make it so node spawns are FATEs as well... Can slap NPCs in all of those, but like regular FATEs the NPCs would have no real impact in the outcome, it would be up to the players to complete the FATEs, except unlike regular FATEs PvP could potentially be involved if other players for the rival Grand Company are present...

Done, much of the spirit of Secure/Slaughter remains, but now we can get in instantly to mess around there... Change winning a match to winning a FATE as far as achievements/rewards go... Perhaps work in something new to create interest in the area... Would be interesting IMO, and much better than leaving the place to gather dust...