Box sets are shown as a long list of tracks, while most box sets (beatles, marillion, king crimson, jethro tull) are made up of logical subsets, main album remastered, main album remixex, demo tracks, live recordings, etc.
Someone suggested using WORK and PART, which were intended to define classical works and its parts. This seems to work, you get your logical overview, nut the main drawback is that now the WORK is seen as the composition, not the tracks itself; this is ofcourse not what you want.
Could Roon use / define another meta data string to support this: combine a number of tracks into a logical subset, but where the individual tracks remain to be seen as composition.