Purely a cosmetic change - being able to add a spacer to the side of arbitrary tracks in the mixer would make it much easier to visually group sections of a mix. As an example at the moment we have left, centre and right zones and there’s a space between the left zone and the centre zone. This separates the two zones nicely. Adding spacers would allow separation of groups of tracks (eg vocal, guitar, etc.) A step further would be to allow spacers underneath tracks in the arrangement view, but not sure that’d be as useful.
Mike