Seen many attempts at "Brand/Series/Game/Fandom OS" over the years, and now i wonder if it wouldn't be better to spend the effort on theming engines or something over a base but functional distro, and then have a gallery of themes to choose from that applies them on everything from the bootloader screen up to the mouse cursor. Want to switch to some other Brand/Series/Game/Fandom? Apply this and reboot, you get the other one. Like the ancient MS Plus but much deeper since Linux allows for a lot more these days.
Plasma themes are a lot of that already done. I don't think it would be too much work to make a script and a UI to automate applying a Plasma and a GRUB theme, at least compared to writing an entire theme engine.