I started multi-quoting, but then stopped, too many things to quote, so I'll just sum it up.
The picture about the Spartan warriors? That is still falling in the category of shoulder-long or just above shoulder long hair for me.
Long hair starts for me around mid-back.
I have worn armors for LARP and when not playing an NPC I had a backpack. NOT trying up my hair resulted in: hair getting snagged in armor parts, belts, backpack, broche holding cloak together and other stuff. => Things which might or might not hurt a lot, but even just the sharp pull at your hair can be fatally distracting.
As for helmet: Nope, never wore one, cause my head is apparently too small for 'normal sizes' and I didn't feel like stuffing it out. Also, I would have had to put my hair up again anyway if it covers the neck as well.
Also really? You wouldn't care if the hair isn't animated as long as it's there?
I sincerly doubt that. Just imagine you walk towards the edge of a cliff with your group to grab another ingredient growing there, a breeze lets your cape or cloak flutter, making it look epic stylish and then... there is the helmet of your hair. Stuck stiff to your head. Or perhaps animated slightly at the edges.
Animating long hair is a pain, even if you divide it into strands. And personally, I really don't want my graphics card waste space to see calculate just the most natural fall and flutter of long hair when they excede a certain hair length.
Bioware does well not to include over-long long hair in the game unless they get around animating it right. I think it would be bad to their name to create this pretty awesome looking game and then add a hair helmet to it.
If they do put it in, I might actually consider it for a mage, depending on the style. I kind of doubt it thought.
If those kind of hair styles are in thought, I am expecting at least the flexibility and animation Sims 3 hair head, when I quickly swirrled my Sim around in the creator mode.