Another way is to abandon original basic resolution (only for software at least).
Will be only two options, resolution and pixel size. Pixel size can be any number that is divisor of both screen sizes.
Basic resolution will be screen size divided by pixel size.
The problem with that is that many areas (such as the Geoscape) look terrible with expanded view because the menus and assets are made for 320x200. (See attached) The battlescape is more or less the only place where an expanded view looks fine. The game is made for 320x200 - that should not be abandoned.
Thing is - "original" doesn't mean much. 320x200/480x300/640x400 means exact and fixed resolution, and "scaling" using stretching algorithm. "Expanded" - meaningful term, but it makes this line too long. And we're short on space.
My view is that the end user doesn't need to know that Original is 320x200. All they need to know is that it's the default, unaltered view of the game, and that Expanded lets them view more than that.
Also, in my case, I said that "Zoom 2x" would be stripped from the title in the dropdown menu and put into its own slider. That way there's room for "Expanded" alone.