I feel we need to think about how something if developed and what things need to be set in stone long long ago, before you can start looking at how parts get made and work together.
It's entirely possible Apple had many new great ideas 6 / 12 months ago which would make the headset better, but by then too many aspects were already locked down, and 3rd parties were already making prototype parts based on the locked down designs.
It's not like a small company making clay pots where they could just stick another handle on the side a few days before they go on sale. This has to be finalised long long ago.
So of course, Apple will have a team right now, deep into the next model design, taking into account all the aspects that did not make it in time for the 1st model which needed to 'get out the door'
I often feel this is why often there is a big leap between 1st and 2nd gen devices, as the 2nd gen is the one which has all the things they could not get into gen 1 during the initial development of a product.
Plus of course, depending on timeframes, you are going to have a ton of actual real world feedback from the 1st few months gen 1 is out that, time allowing, can be fed back into the development of gen 2 or even gen 3
It will be interesting what timeframe new models come out.
I for one, and I know I was not alone here never thought the Apple watch would have been updated so fast after it's launch.