Might be more work than you expect. True, Fandom websites do probably have the same target audience as the programs you mentioned but that doesn't mean doing it is easy. There is a lot that goes into making graphical interfaces for novice/first-time users and even more when you give them the option to move menus around. Generally speaking, the easier it is for users, the harder it is for programmers/designers.
Edit: Just to be clear, I am not a fan of the switch to vertical either. I think, once Fandom got users used to horizontal, they should have stuck with it. I am just saying most (not all) of the websites/programs I am used to pick one and stick with it; not offer the user a choice. A fair number allow you to rearrange the tools but it still stays either horizontal or vertical.