Or, they're just being lazy/economical and reusing old stock.
The new system design I want to see is an update on the 11" MacBook Air or the 12" MacBook. I'd like to see if they can get a clamshell with good battery life and decent performance under two pounds and just wide enough for a full-size keyboard. The 11" MacBook Air is still my favorite laptop I've ever owned; I'm sad they discontinued it and didn't refresh the design. Maybe it can come back with an M1 or M2 chip, though.
Why fuss over driver compatibility if the performance on Apple's graphics cards blows away the competition?
Anecdotally, there was a step function between 3 lb ultraportable laptops with 12-13” displays and the 2.2 lb 11” MacBook Air. It was the most grabbable, portable computer I’ve ever owned with enough CPU power to handle my Computer Science coursework. It changed my relationship with my laptop. It no longer felt like a lump in my bag that needed to be handled carefully, like all the previous plastic bodied things I’d owned.
I have since used a 13” Air, Pixelbook, Samsung Galaxy Chromebook (until it died), and I’m typing this now on an iPad Pro, and I still miss that laptop.
The HP Dragonfly looks real nice, maybe if I put Linux on it. It’s also $2200 for decent specs though, whereas the 11” MacBook Air was a comparatively reasonable $899.
The efficiency differences with a 37 W max power draw is negligible.
For the first release, the approach here is pretty obviously: The minimum changes needed to existing machines to accommodate the M1.
That approach makes a lot of sense because it minimizes the time to market. It puts Apple silicon in people's hands as soon as possible. That's important because the sooner that happens, the sooner the software will be updated for AS.
Think about it: the alternative was to just make people wait for the redesigns, which will take a year or two more.
And the redesigns are coming... judging by all that empty space in that mini, they will be dramatic.
Apple most likely has the oomph (financial and human) to do both at once. However only changing one thing makes troubleshooting way easier if things go wrong. Here the case and overall machine design is a known entity.
They did this with Intel, too, more or less.
Also, historically the Mac Mini has been a split line; one SKU with a low power (~20W) chip and one with a 45W chip. But otherwise mostly the same. It's fairly plausible that they repeat that here; when the M1X or whatever shows up I'd expect to see a more expensive Mac Mini SKU that has one.