Signal Beam feels like a move that is an excellent choice as a machine/tutor option: an unusually-typed move available as an option to a similarly unusual (but consistent) list of Pokémon. Sure, it's a Bug-type move, but it's hardly associated with Bug Pokémon aside from Volbeat. I really like that sort of flavor; Megahorn is in an idential boat, and it was added as a TR. Its Grass-typed clone, Power Whip, was added as well, and I think it functions similarly as a move that isn't necessarily represented by its type, and as such works well as a TR.
I think machine/tutor moves for coverage come in two varieties, generally: strong moves that are given to Pokémon of the same type and those of a related type (see Ice Beam with most Water Pokémon, or Rock/Ground moves generally), and those that are a little weaker but have a wider spread to give different types greater coverage. Notably, Psychic/Bug/Fire is perfect neutral coverage (ignoring Heatran), and with Mystical Fire as a machine move, Psychic types could have a pretty solid set of moves that isn't the usual Psychic/Focus Blast/Shadow Ball (or Thunderbolt).
Unfortunately removing Signal Beam means that the already coverage-starved Electric Pokémon lost one of their few options. Grass Pokémon also tend to struggle for coverage, and SwSh kind of delivered with Pollen Puff. Unfortunately, it's ALSO Bug-type (meaning it only directly gives them an option to hit opposing Grass Pokémon), and it has such low distribution that not many Pokémon that get it can use it well. At least it can function as a healing move in doubles.