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Back in the 2e days I had decided already that many elementals had intelligence and some sort of society. It appears 4e is going that route seeing at all the elementals are humanoid in shape and holding weapons.
I'll use the Fire Archon right alongside my Hound Archons. If I'm given a mini and a 3.5 statblock for a critter, I will probably find a way to use it. I've enjoyed the late-3.5 monsters in MM4 and MM5, and this guy (the Fire Archon) seems to be from the same design school.
Though if I needed some brand new generic fire elemental-like stat blocks for some reason, I might find some use for said stat blocks... assuming I even remembered their existence and where to find them...
On first glance, most likely not. If I were to do so, my first step would be to remove the ability that triggers at 50% hp- I despise the mechanic of abilities automatically triggering at 50% hp.
Actually, it's quite possible. One of enemy organizations is a religious organization devoted to Pyremius, one of whose porfolio elements is fire. The cult's tactics are based around assassination primarily, but they might send some Fire "Archons" after the players, or have them guarding they're temples.