As far as the power armor is concerned I don't thing that it needs to be strictly tech themed although that is by far the most common kind of power armor. However I could also see womething more akin to a Dr. Fate style character with the armor being the magical creation of one or more beings. yes I know that it's just the helmet that is "enchanted" in Dr Fate's case, possessed would be a more accurrate term but the concept still applies.
Power armor could also, loosely, very loosely, be applied to symbiote style characters. Not specifically Venom and Carnage but think more Guyver and that kind of symbiote style of armor.
Now one thing that I have gotten into heated arguments in game about is where an AT/power sets starts/ends and where costumes start/end. I am a firm believer that power armor IS NOT A COSTUME. From a game design stand point you can only give so much to players before the whole thing becomes overly unwieldy. I do appreciate wht the game is and what it does have is one of if not THE best costume creators that there is.
However, as with other power sets/AT types you can only let so much go when it comes to what is a necessary evil in order to play a specific character type in a game. I mean can you immagine if your concept for a character was to have optic blast but every ranged power set was designed to come from the feet? While an admittedly silly example it shows that you could never play an optic blast style character. This is kind of how I feel about my favorite kind of characters which are power armor (Iron Man styling) characters. Costumes only go so far when it comes to how happy I am with my overall power selection.
The next thing that has to be discussed is what kind of power armor is going to be the basis. Are all power armors going to be forced into options like the wolf spiders if they go crab spider? Will the "power armor" all be 9000 foot tall gundams? Will they all look be forced into a overly narrow idea of what one creator believes that ALL power armors should look like? This I think is one of, if not THE biggest issue with creating power armor as an AT or EAT. Anime is huge but not everyone enjoys it and certainly not everyone is addicted to it. Thus this creates a big issue with what is and isn't power armor based strictly on visual appearance.
For me personally, I would say that anything that we wold have access to in the game, ie anything under 10ft tall, would be power armor. I even see the Malta Zeus, Hecules and Titan enemies all as mechs or mech sized beings.
Now as far as what the actual powers are, I have a write up somewhere buried deep in these forums that I did but is never got any traction as I was suggesting an EAT and not a power set. The suggested powers here are for the most part fairly well laid out. It would have to, IMO, come with costume requirements but that's just me.
