I've been thinking on the helmet issue.
For Yamatai, we're used to the "biker's helmet' style, but as pointed out before, it leaves the necks fairly frail. Even if you protect it with an armored collar, any good power armor-level strength physical hit to the head would more often than not be good justification to break a human's neck.
It made me think about the issue, and I realized that present day astronauts do not work with helmets like that. When they go out in space, their heads are within a bubble-like transparent canopy.
At first, I figured that this sort of thing would be bad for our power armors due to not being able to turn the head around, look above and such... but then I realized that current technology allows for the armor's HUD to provide all-around 360 vision. The user could just glance up by looking up the armored canopy covering his head. It'd give ample room to justify sensors and life support components too.
That 'practical' points however makes departure from the humanoid Samus Aran/Bubblegum Crisis hard suit-style and goes further toward the Meltrandi power armor from Macross or mechas more like
this and
this in Bubblegum Crisis 2040. It's certainly going to depart humanoid form more.
It's more a styling decision than anything else. Staying with the Motorbike-style helmet would still, as long as it's the desired look for people wanting to wear Yamataian power armor. What do you guys think?