Something like X resources gave the user deep configurability indeed; what's more, because they lived on the X server they communicated user preference to even remote clients.
A graphical tool to allow users to set preferences through X resources, similar perhaps to Visual Studio Code's preferences pane, might be a great way to allow users to tweak their apps with power and precision.
Of course, literally no one uses X resources these days, all settings live in XDG_CONFIG_HOME. And it's all moot under Wayland, which doesn't even allow remote clients.
A graphical tool to allow users to set preferences through X resources, similar perhaps to Visual Studio Code's preferences pane, might be a great way to allow users to tweak their apps with power and precision.
Of course, literally no one uses X resources these days, all settings live in XDG_CONFIG_HOME. And it's all moot under Wayland, which doesn't even allow remote clients.