I like this three-row design. When a new MW version comes out, simply a new row needs to be added, and one can see in a glance that the extension doesn’t officially support it (yet). Was it one row, it would be less clear that even though an extension supports a bunch of MW versions, they’re all years old. Also, it’s easy to drop MW versions no longer supported by Wikimedia (i.e. versions that themselves get no security updates anymore), so no longer relevant information doesn’t clutter the infobox.
That being said, I’m not against using one parameter for all versions in code, given that it’s still displayed in three rows as now (neither am I definitely for it, though); and I think categorization is a good idea. Some documentation would also be useful, especially specifying the valid values, which would be needed to implement categorization (as well as to make this part of the template translatable).