Various sources say (I don't know how conclusively) that Paul Barth's fretless bass - variously branded Bartell (his own company), Lancer, Contessa, St.George, Acoustic (“Black Widow”) and Hohner - predated the Ampeg by a year (1965). Certainly coeval with it, at least.
But, to reinforce your later post, it is true no-one here ever claimed the fretless bass was a Fender invention.
As for the 5-string bass, there is a connection between the Fender V and Jimmy Johnson's first BEADG bass: one specific reason why he ordered from Alembic (besides them having established a name as makers of custom boutique instruments) is that they had already made custom fivers. Only, they came tuned EADGC, just like their Fender predecessor (but with 9 more frets, so they were authentic extended-range instruments relative to the traditional 4-banger). As far as I've read, Jimmy's own bass came like that from the shop but, being a GHS endorser, he'd managed to have the string company make a 120 low B that he installed on the bass after reworking the nut slots (he did some work at the bridge end as well).
Back on topic: if Fender managed to put out an all-new, or radically redesigned model that combined some retro-futurist lines (in the same vein as some Duesenberg, Reverend or Italia models), a fan-fretted board could be visually integrated without sticking out like a sore thumb. I could see it being made for a limited time, like the Rascal and, depending on the sales performance, it could lead to more mass-produced things.