Bug/Rock is actually not that bad of a typing, as long as the pokemon is specialised towards revenge killing and has very high physical attack to deal a lot of damage with STAB U-Turn (think M-Beedrill). As for other type combinations, Bug/Water, Bug/Psychic and Bug/Dark haven't been touched on yet by GF and I can see them fitting the original Genesect, though the latter two are pretty bad typings and would require great everything else for it so it's not completely outclassed by modern Genesect.
I'd actually prefer if Techno Blast was replaced by a status move rather than an attack. One idea I have is combination of Recover and Refresh with only 5 PP as a drawback. However /Rock has no offensive moves to work with its typing, so it either needs to get Stone Edge in its levelup movepool or have Techno Blast change into an unique Rock type attack. Or just get Rock-type -ilate, but that's absurdly broken with Extreme Speed.
Best ability is probably Tinted Lens, especially for /Rock and /Dark since they have two common resists each.
On that note, I'd prefer if this were an alternative form with same BST and ability to hold item rather than yet another in-battle evolution. Won't bother with exact stats, but it wants lower defenses in exchange for heavy increase to Speed. Could also use dropping Special Attack in case of /Rock one.
Also GF should finally fix Techno Blast for modern Genesect because it's still useless even after its Gen 6 buff. Needs to get 20% extra damage boost when holding a drive.
