One way of true environmentally-friendly innovation could have been to find a way to attach the SSD chip so that a user could safely replace it, though, with little additional space.
I don't think these are real problems. The M.2 device would take up space you could have used for the PCB, but then you would have had to use that PCB space for the chips that are on the SSD.
The SSDs in current Macbooks do around 3GB/s. NVMe Gen5 does 14GB/s. The speed-of-light latency from any kind of connector is going to be totally irrelevant compared to the latency of the flash controller itself. There is no performance concern. Power is the same; when idle the link goes to sleep, when in use the connector is negligible compared to the device itself.
Heat transfer doesn't even seem related. If you want to improve heat transfer from the SSD then you put it into thermal contact with a heatsink or the chassis, which you can do regardless of whether it's M.2 or not.
> One way of true environmentally-friendly innovation could have been to find a way to attach the SSD chip so that a user could safely replace it, though, with little additional space.
The only real space requirement is the size of the connector itself, which is on the order of 50 square mm in a PCB which in a 12" laptop is some tens of thousands of square mm. <0.5% is "little additional space" to begin with.
Obviously you could design a connector which is even smaller, but the premise would have to be that that's even a real problem.
The idea that a PCB gets larger with an M.2 slot is truly insane.
For an iMac, though, they have a bigger thermal envelope and no battery. It seems more reasonable. Apple even did the software engineering necessary to support the Mac Pro.
That would be Apple’s counter-argument right there. Want Linux on your M1? Get a Mac, not an iPad. Want swappable storage? Get a Mac Pro, not an iMac.