But the point is if you're ok with a Rasperry Pi class computer, why not just put it in the phone? And indeed, the Pi is outclassed in performance by pretty much every Android device in existence.

You're already carrying your phone with you. There might be some value in a "shell" with a Raspberry Pi level computer in it, but in that case I think you'd see the opposite happen to what you're suggesting: The shell using the phone for additional computer power when present, and the Pi class computer simply being a way of offering very basic dumb terminal capabilities when no superior computing device is present.

> Historically though, things such as laptop docking stations and laptops with detachable tablets have never really taken off and I imagine this could be a case of the same.

Historically, laptop docking stations were a big deal for businesses, and "laptops with detachable tablets" are where the tablets were/are actually usable is a very new thing. I don't think you can draw any conclusions from that.

When consumers are aggressively searching for the lowest price, and in general lack the sophistication to tell what the performance is, you generally end up in a situation where even a buck or two can be the difference between a product that sells and doesn't. Sometimes the sophisticated option can be squeezed right out when the masses can't tell the difference... ask me how I feel about the inability to buy anything but TFT screens in a laptop sometime.

That is true, people often have crappy taste when it comes to quality (or just low budgets). However I think there is a big difference between buying "a laptop" and "a laptop that doesn't do anything unless you plug a phone into it".

Look at the iPad.

Tablets never took off before Apple did it right, with a similar look and feel as other apple products.

It's all about the experience.