Nothing, in my opinion. The problem is many tech nerds want change for the sake of change, as hardware does more than any really need.
"Tech Nerds" like myself (apparently...), don't all want to elicit change for fashionista points, looking cool at the coffee shop, soaking in the occasional nod over a matcha latte.
The redesign, or rather *design tweaks* I personally am looking for are functional:
1. smaller form factor by reducing the bezels. 12" notebook is a sweetspot - as I enjoy taking my ipad pro around - and once did the air 11."
2. mini LED display with potential further battery savings.
3. updated webcam. The current one's optics are just flat out of date.
3. rumored darker chassis - less of an announcement in public space.
It's also worth noting not to put the cart before the horse. Apple doesn't tend to change hardware to placate vanity. The imac line hasn't changed largely in outward appearance in over a decade. It works and works well. So when Apple does decide to make a physical change to it's hardware, there tend to be functional reasons guiding the aesthetic change, that I choose to pay attention to.