I'm still not going to use windows or linux. Don't want to be an IT guy on the side just to keep linux machines working. This may not be obvious to some unless you try to use printers and scanners that are more than 5 years old and what them to be on the network. And, you don't install virtualization tools like vmware that require compiling and loading kernel drivers which ends up being incompatible with new OS releases...etc.
Windows is just too much of a painful acceptance of mediocrity and apathy in product design for me.
For the SSD, no. For the memory, yes. The memory lives on the same chip as the CPU and the GPU, it's even more tightly bound than just being soldered on. The memory being there has legitimate technical benefits that make it much easier/cheaper for them to reach the extremely high memory bandwidths that they do.
Same reason as a) GDDR on dGPUs (I think I read somewhere that GDDR is very much like regular DDR, just with much tighter paths and thus soldered in) and b) Framework Desktop (performance would reportedly halve if RAM were not soldered)
SSD reasons I seem to recall are architectural for security: some parts (controller?) that usually sit on a NVMe SSD are embedded in the SoC next to (or inside?) the secure enclave processor or whatever the equivalent of the T2 thing is in Mx chips, so what you'd swap would be a bank of raw storage chips which don't match the controller.
The soldering does serve a purpose though, the shorter traces allow for better signal integrity at higher speeds. This isn't something special about what Apple is doing though, Intel and AMD are doing the exact same thing with the exact same LPDDR5 chips on their respective APUs.
HBM is still almost purely reserved for datacentre GPUs.
No. There is a reason for it but no, it's just soldered on the same carrier board as the APU, in order to be really close to it. Apple could have used a form factor like CAMM2 and it would have worked the same, be it at slightly higher cost. The reason is simply to kill upgrade options and cut manufacturing costs - same as for any other soldered ram.