I often have full concerts or interview discs that need a home and “other” always seems wrong as there was never a CD only version. Agree also that “bonus discs” added to deluxe releases should not be in this section as they are clearly part of the original album. But now they would have a home when release as a separate item.
One puzzle though - what about that concert album that is released as CD and separate DVD\BluRay? They will need carful guidelines. I would suggest they stay under “album” - but it is an edge case that will come up and needs to be in the guidelines from day one.