Feels kind of asymptotic to me: they got most of the basics right 100 years ago, but things like derailleurs are a pretty big improvement in terms of allowing an ordinary person to ride over varied terrain. Quick release skewers (grazie a Tullio Campagnolo), lighter materials, clipless pedals (for racers)... have all been incremental improvements. More recently, tubeless tires on mountain bikes are a big improvement in my enjoyment of riding off road.