The bassoon in its modern form, or something quite close, was birthed in the mid 1600s.
It's hardly changed since then not because no one could think of something better in that range, but because every "improvement" ended up being a different instrument; nothing could do what a bassoon does better than the bassoon. Maybe the contrabassoon for us ultra-low heads, but it can't dance in multiple octaves the way a bassoon does, either.
If an instrument works, it just works. Overall, the varieties of design of the bass guitar are relatively minor: it's an electric stringed instrument centered in the range of the contrabass, and designers experiment with it in much the way they did with brass instruments (developing keys, and then rotary & piston valves to control them) and every other range of instruments out there.
Those changes all happened over centuries as far as a new design really coming to dominate. The bass guitar has not been alive for nearly a century. Ultimately, if the math and the playability of fanned-fret design wins, it will overtake several centuries of fretted instruments (but hey, the equal-temperament-capable grand piano overtook several centuries of harpsichords and clavichords and the like, so that's not impossible!), and if the music it can make provides a forward direction in innovation, then it SHOULD take over.
Musical instruments experience long periods of evolution punctuated by moments of sheer revolution, as I think Jean Paul Sartre wrote. Maybe it was John Paul Jones? One of those Johns or Pauls
