QuickPlay Frontend

If an empty folder has subfolders, it could display the contents of all of them (like virtual folders). Is there a reason why it doesn't work like that?

the reason is that it wasn't considered when written. There is a dichotomy here however: sometimes you want that behaviour, but sometimes you don't. And I don't think this is just about QuickPlay, folders can sometimes be seen as collections of their constituents but sometimes be seen as entities on their own (that can contain other collections, but are themselves a collection).

An example of wanting the other behaviour is if you have an older collection of the same roms, that you keep for a certain reason. You want it to be a subfolder of 'sony playstation', you don't want your 'current' and 'old' sets to be at the same point in the folder tree, you want the 'old' to be attached to the 'sony playstation' folder, but not collected into the parent

Another example could be if you had .pdf manuals for your 'sony playstation' games: the same rules as the above apply: you don't want the manuals to be at the same folder level as the games but you do want to 'attach' the manuals to the game folder

You can achieve manually the effect you want: copy the romdata folder in windows so you have two of them, and consume one of them in quickplay by dragging the roms into the parent - you can do that with as many subfolders as you like (you have to clear up the empty copied folders in explorer after so its a bit messy)

But if you hardcode your option, you can't then go back to achieving the other option - there would have to be a toggle like "romdata folder type" in the options, and that sounds a bit complicated for most users, so i'd probably want some better way for advanced users to achieve your option, rather than forcing all users to understand both options in order to understand the folder settings page...

be interested in your thoughts

The toggle could be in the General Options window: "Show subfolder contents in nested folders"

what happens then if the feature is on, and you add content to the root folder?
and what happens if the feature is off and you turn the feature on, when the root folder already has content?

I think the simplest solution is to show the items in the subfolders in addition to what you've added / will add to the parent (if you add anything).