I wouldn't say GoPro is on the decline, necessarily, though they have leveled off, IMO. There's a certain ceiling to their product, and I would argue that it's been reached to some extent, but it's not like there isn't a GoPro camera stuck to every flat surface possible at sporting events all over the world every day.
I guess I don't see nearly as much overlap between a GoPro and an Osmo as others. To me, the Osmo's power is in the rig that's built into it, whereas GoPro's rugged construction and wide aspect ratio allows it to do things you simply wouldn't even bother attempting with something like an Osmo. I would imagine there are people who have been "making do" with a GoPro that would love to use the Osmo instead, but I don't expect to see one suction cupped to a surfboard.
I guess I don't see nearly as much overlap between a GoPro and an Osmo as others. To me, the Osmo's power is in the rig that's built into it, whereas GoPro's rugged construction and wide aspect ratio allows it to do things you simply wouldn't even bother attempting with something like an Osmo. I would imagine there are people who have been "making do" with a GoPro that would love to use the Osmo instead, but I don't expect to see one suction cupped to a surfboard.