Currently, DSpace's "full" community-list rendering uses referenceSet objects. These, in turn, result in individual METS document generation calls, which can cause a very slow page load for larger repositories. In order to improve load times, while maintaining the "full" list style, the necessary information can be pre-loaded into DRI elements instead of referenceSet objects.
As is done in full-view this new view, this improvement provides the item count (if configured) and comm/coll description in the DRI. In addition, for Mirage2, it brings the collapsable structure to the non-"full" view. Original Mirage style has been left unchanged (but XSL has been updated to render new DRI structure).
May want to consider defaulting xmlui.community-list.render.full to false. If developers desire additional DIM or METS metadata, they can toggle to true. This should improve performance overall (not making N METS calls), while not degrading most systems with "full" view currently enabled.