Maybe this would break the tradition, but I think this term should not be dependent on the player count, but on the size and type of the game, something like an opposite of coffebreak roguelike. ADOM, Angband, NetHack, Crawl all have several hundreds of items, monsters, lots of races and classes to choose from, several days are usually required to win the game, and in general, lots of options and huge complexity. Some roguelike developers set goals like "I want to create the new ADOM/NetHack/Crawl/etc, but even more complex", and these roguelikes become major roguelikes if given enough time, and some focus on a simple goal. I think Spelunky, DoomRL and probably all 7DRLs fall into the second category, and I would not qualify them as major roguelikes, no matter how many players play them. Both major and coffebreak roguelikes can be good or bad games, and have lots or few players.