It's been said a few times, but I actually think remoraid->octillery is a pretty neat idea. Remoraid is mainly based off of a gun, but it is also supposed to resemble a remora, a type of fish that has a suction cup on the top of its head to hitch rides on animals and, sometimes, boats. That also explains why remoraid was the fish pokemon chosen to be under mantine's wings. Since a remora has a suction cup on its head, evolving into an octopus doesn't seem like that far of a stretch. Also, octillery keeps with the gun theme by looking somewhat like a turret.
For now, the only weird evolution I can think of is flaaffy to ampharos. To tell the truth, though, I actually prefer drastic evolutions, because it seems less like the pokemons just getting bigger, and more like its actually evolving.