This is my main complaint with the design. Comfort is king for things you wear on your face, and a lot of the design decisions compromise comfort. If I was designing v2 I would delete the external facing display and glass cover, move all processing to the battery, and ship a rigid strap.
None of the arguments against putting the processor in the battery make any sense. It adds latency? No it doesn't, if designed correctly, and I guarantee you can fit the correct design in the budget for $3500. You can't cool it from inside a pocket? The wire is sticking out already, you could add a short air intake to it. It would be too big? I guarantee that size is easier to carry in the battery than on your literal face!
The only thing that makes sense to me is the battery was supposed to be internal and the external battery was a last minute compromise for comfort. Unfortunately I suspect that Apple will go the direction of moving the battery back in for v2 rather than moving processing out.