There are individual pieces of equipment which can do TFs, like the Hornet Ring or Collar of Submission. There are individual pieces of equipment which provide powers, like the three separate pieces of attire that give summon powers, the Magatama which gives a mediocre self-heal power, and a load of weapons which have their own powers. There's a bunch of equipment with unique effects aside from those two categories.
However, I do not expect that there will be full sets that only have effects if all pieces are equipped. The Witch's outfit was unique in having a tf when all pieces were equipped, and maybe there could be other events with a transformation tied to a one-time equipping of a set. If, of course, someone wanted to write one, but given that the Witch's set is, to my knowledge, the only one of its type, I expect there not to be.
And of course, as Wolfram said, you can already swap out your abilities at will. Not all powers are available to you, but you can still use a ton of different moves. The Champ's biggest strength is the versatility they're afforded in their equipment and abilities, not to mention that the Champ can consume basically anything and have it work as a transformative. There's no need to restrict these things to sets for the player.