It has been brought up more than enough up to now, but I am still curious what would be the engine of choice for everyone. Personally, I would recommend either UE3 or Frostbite engine. Both already work well with vehicles (at the very least better than Source) and natively support aircraft. As far as mod support goes, UE3 would probably be the better choice. Frostbite, on the other hand, does the things Empires needs well, e. g. very large maps, 64 player limit, vehicles.
I don't really know anything about engines so I will go with what I am familiar with. Valves stuff works, we are just outdated.
Would love to see Empires on Frostbite, but realistically speaking, the go-to engine would probably be Unreal. Do a Renegade-X pls.
Frostbite 3, but realistically Unreal 3 since EA would never let people make mods ever again. You forgot a very crucial engine Unity, which is starting to show up a lot on amateur 3d games. Someone actually tried to recreate Empires on Unity, it was looking alright (mostly just placeholders) but I think he got bored of it. Still love Source though. For some reason I feel like it's the most realistic looking engine, and that's quite the statement to make about an engine with such low spec requirements.
I would actually hold out to see what Source 2 is like, with the gamble that it comes out relatively soon.
If possible, Cryengine 3 for the lulz and eyecandy, else Frostbite engine, Unreal is nice and all but popularity of the engine dictates the amount of players you can reach with the mod, (maybe I'm wrong about the popularity of the engines, dunno), thus Frostbite.
Frostbite although IF source 2 comes out soon its possibly a much easier transition to it then to any other engine. Still source is built around enclosed environments, unlike frostbite, and would be bad for our mods continued development.
Frostbite would be neat, though I am curious how empires would look as a crysis mod. I think modding for crysis would be easier simply because they already released a dev kit, frostbite hasn't as far as I know. Still the sad thing is the more graphically involved a project becomes, the longer development becomes. Though seeing current empires on a fancy new engine would be hilarious.
Source 2. I already love Source simply for the familiarity of movement and other such aspects. Despite the flaws it has, if someone like me can understand the intricacies of the way the engine works with regard to scripts, models, etc, how everything ties in, then it's pretty straight forward. Unrealscript is much more complex. Add in that Source 2 will have really impressive Steam integration, probably work on all platforms and the fact that they'll make it as accessible to indie developers as possible in an effort to corner that market, I feel like Source 2 will really be a game changer. Obviously I'm assuming Valve won't repeat the mistakes they made with Source 1, which might be a stupid thing to do on my part. But I really feel like Source 2 will be Valve's way of locking Indie titles onto Steam only, so they'll have to do a good job with the SDK and whatnot.
Currently it's only available for selected EA partners like EA Black Box (NFS: The Run) and Visceral Games (Army of Two).