There will always be tinkerers and people who want to customize their stuff to their personality, but I think the majority of people don't want to tinker, they want to "get shit done" and the standard wallpaper and theming of stuff now days is visually pleasing enough to not mess with it.
Personally I couldn't care less about things being "visually pleasing", to me this is an accessibility feature. People with sight issues or dyslexia might want to use different fonts and weights, they might want high contrast colors, etc. The aesthetic personalization opportunities are second to that. More importantly: this isn't hard . They did it in Windows 3, an OS that had an 8MB install size and required a mere…
Are there particular ones that are missing when it comes to dyslexia?