I get the premise, I really do, and I'm personally leaning towards single purpose devices, at least for music - but honestly, what value does the typewriter actually provide?
Focus on writing (typing) and only that; in a hypothetical "me as a writer" scenario, doing it on a computer makes it easy to alt-tab to look something up, and before you know it there's more time spent on that (and not necessarily focused on the original question) than the writing.
It's just the sheer weight and clankiness of the typewriter that I can't justify, why not just a really old laptop with not internet access?
Arguably, separating different tasks in real life is a positive. If one spends a lot of time writing and wants to separate their leisure time to their writing time, having a dedicated (and limited) machine can be a positive. Like having a separate room to work in.