There are currently 3 sub-objects levels for editing a mesh: Vertex, Edge and Face. In practice we also manipulate a lot a mesh thanks to the various elements it is made of. An element is a set of faces that is not connected to some other sets of faces inside the same object. We can already select such an element by first selecting one of its entities (a vertex, edge or face) and then press Ctrl + L.
It would be very helpful, natural (and even consistent since this level is already available in the UV editor under the name Island) to have a 4th Sub-Object mode to be able to work on elements of a mesh.
3dsMax has such a mode, it is really consistent with the modeling workflow and would have all its legitimacy in Blender.