I think the helmetless option should be a given. Not as some kind of reward, but as an option that, after all, exists in nearly all MMOs (the "hide helmet" option). You don't spend time choosing your character's face and hairstyle only to have it hidden forever by a helmet! Perhaps the customizing could come in the "light" vs. "heavy" helmet variations. Don't misunderstand me, I'm not saying they should have different game effects; it's just to use those varieties that after all are shown on some (admittedly more modern) minis where the fully closed helmet has been replaced by some kind of a filigree covering the chin and forehead of the character. Also, several depictions of Eldar show some fur and/or feather adornments. Besides the sashes and all that, having some of these could look great.
That's a good point that I haven't seen discussed much. The planet seems like it would be quite habitable, so going helmet-less would make some sense. Although, I would hopefully expect to see some armor sacrifices to your head protection from going helmet-less. It always seemed silly to me that only the most important characters decided to forgo using their helmets and exposing their most vulnerable areas. For a war simulator, it seems that teaching people to always wear a helmet would be one of the first rules, remember Starship Troopers? Otherwise, having the option does sound like it should be a feature, at the very least for faction hubs where you should be able to relax a bit.
Bear in mind that lore-wise, different aspect shrines have different colour schemes now, after the advent of the last codex... I think being able to change you armour colour scheme would be cool if it is possible.
Just putting this out there. Autarchs do follow a path, it's not as official as the path of the warrior or seer, but the path of the leader is still technically a path. One who follows multiple paths of the warrior, exploring the shrines and learning all aspects of Eldar warfare to better lead their kin. Even as they stand as an Exarch of one shrine they still bear their wargear (or at least it has never been stated that it is ever given back or removed.) Yriel is the prince of Iyanden, and is the only "permanent" Autarch, however others like Kayleth would retain her wargear at all times, despite being only an Exarch back on Alaitoc.
It's worth noting that an Autarch is not "stuck" in the path of war like an Exarch, he is merely one who has walked most of them and has great experience of his own (so not conferred by the Exarch armor). I figure that Autarch wargear is it's own thing rather than that of any given shrine, at least in terms of armor.
Autarchs cant be exarchs... they are both lost on different paths, an exarch being stuck on the path of one aspect, the autarch following all of them
I know, I was just pointing out that the Autarchs actually follow the Path of Command, rather than all of the Aspect Warrior Paths.