People generally want slimmer and more battery-dense products

I call BS on that one. People say they want slim electronics and the first thing they do is to slap it in a protective case. It's like SUVs and light trucks in the USA. People don't even have the choice anymore because smaller cars are not as profitable, so then Ford goes to sell one gazillion F150s to soccer moms and then they claim "we are just fulfilling the demand of the market".

My Fairphone seems bulky in comparison (and it is), but it is small enough that I can have it in my pocket.

(laptops) the best you get is RAM and maybe MXM

Is it really? With things like M2 slots you can get separate wifi adapters, fast storage. With Thunderbolt, we don't even need a high-end graphics card in the laptop. We can do plenty with an iGPU and have an external, upgradeable GPU for those that want to game or do heavy work.

which means at best you’re swapping pretty big chunks of a smartphone at a time.

Fine by me. If we break down as CPU/storage/camera module/"everything else board", then it's 4 modules. Which is a lot more than what we are getting now and it's the complete opposite of what manufacturers are giving us.