For example the "fusion" of Bach with jazz by some Jazzman...Or the encounter between Ali Akbar Khan and a jazzman... They are more musical encounter event and interesting , more than the development of "a new fusion genre" as such ... the event will not be repeated on a long term creating a new language replacing the two which fusionned for an album..
I once attended a concert that featured Ravi Shankar with Bud Shank, Dennis Budimir and various other LA Jazz players but was not that impressed. To me it sounded like two traditions moving in parallel.
On the other hand, I very much enjoy the Indo-Jazz "fusion" of Shakti, which seems to me more Indian than Jazz, overall. John McLaughlin seriously studied the Vina. In fact, he said he was falling in love with it to such an extent that at one point he had to ask himself whether he wanted to make it his main instrument and give up guitar. He's also studied the Indian system of keeping time or Tala. So, he's done much more than just "dipping his toe" into Indian music.
My parents had some recordings by flautist Jean Pierre Rampal and Andre Previn that attempted to fuse Classical with Jazz but I never cared for them. It was all too polite and safe.
Vocalist Savina Yanatyou has some recordings on ECM that attempt to bridge Jazz with traditional middle eastern music. I like them but they don't sound very jazzy to me. Oudist Anouar Brahem has attempted something similar with his ECM releases.
I'm left with the impression that a true fusion is rare. Ironically, the fusion of Rock and Jazz may be the most successful to date, even if some of us don't find it that compelling. A lot of Fusion records sold during the genre's heyday, for whatever that's worth.