There do exist corresponting metric sizes in Europe:
5x7" will fit into a 13x18cm-holder. All other combinations do not work and require a the corresponding holders. The metric film holders do have the same exterior dimensions but different guides for the film.
9x12cm is still popular in Germany (if one can claim this within the niche of sheet film at all) . IMO, 9x12cm has a more pleasant aspect ratio than 4x5" and fits better in most paper sizes, too.