Our company [0] developed a cutting edge computer vision system focused on detecting cardio machine exercise cadence (hyper specific!) and became the only reliable camera-based solution to do so. We then tried to generalize to all exercise motion (rep tracking, a still unsolved problem), achieved mediocre success, and put the exploration to sleep later because we think waiting for other technologies to mature would be easier and faster (better 3D cameras, AI pose models, etc). On the other hand we've picked other niches that meet our business needs to expand our CV R&D into, with pretty good success but mostly just for internal use (video content creation tools). More importantly, we're still the best camera-based indoor cardio detection tech out there, and that's a big part of why we're still alive as a bootstrapped business founded in 2010.
Quadruple down on your niche first!