Yeah as Gladius says, I've never seen a half-caster Bard not in official material, not in unofficial material, that wasn't complete and utter trash of the most crummy kind of a mechanical level, and usually not at all fun to play either (I say this as someone who has played multiple Bards in every edition from 2E to 5E, as well as various other D&D-related games).
Could it be done? Yeah, probably, with a sufficiently genius designer, who can manage to work out how to make up for losing god knows how many incredibly powerful spells. Is it remotely likely to happen? Noooooo. I've never seen anyone manage it.
And what's interesting to me is, the people keen on the idea of a half-caster Bard? Almost universally don't like or long-term play Bards. They're just offended by the concept of full-caster Bards, aesthetically. They liked it when the Bard has to be this passive loser-guy in 3.XE and Pathfinder, singing for the benefit of everyone else, not upsetting the Wizard by casting better spells than him. To hell with that! I started in 2E. The 2E Bard might technically seem like a half-caster, but in practical terms, no, because of XP. I was literally casting 5th-level spells before the Elven Fighter/Mage in my party was, back in 2E, and not far behind the actual full-on Mage.
I mean to be fair, only one Bard sucked, and that was the 3.XE Bard. 2E you levelled like a rocket and had access to a really good selection of stuff re: fighting, sneaking, and spelling, with music and lore to complete the package. 3.XE, you were just terrible. This awful character who had been shoved into this support-hole, but who wasn't a full caster like the "support" Cleric (who also had a much higher AC, better HP, better spell access, same BAB, and was just missing some janky music abilities, which his spells could outperform anyway, for the most part). At least you had spells and thanks to LFQW you weren't the worst character in the party. 4E Bard was extremely solid, fun, and well-themed. 5E Bard is a powerhouse like all the 5E full casters and is great fun to play.