Baldur's Gate 3 is very similar to other massive RPGs in that a treasure trove of interesting plots and recruitable companions were left on the cutting room floor during development. We already know that Larian had to cut a werewolf bard companion during development – an absolute crime considering the game has no bard representation among its companions – but it was recently revealed that you could originally recruit one of the game's main villains into your lovable gang of misfits.
Speaking with IGN following the Secrets of Baldur's Gate 3 panel, which saw the reveal that Astarion was almost a Tiefling rather than a High Elf vampire, Larian Studios head Swen Vincke began talking about several other features that were cut during development, one of which would have been a recruitable Ketheric Thorm who would have started out hanging around your camp as an NPC.
According to Vincke, when talking to Ketheric, you can see "a moment where he breaks", which was originally where you could begin trying to convince him to join your crew. Ketheric would then join your camp as an NPC who would give you vital information about Orin the Red and Gortash, eventually building your trust with him and leading you on the path to having him become a playable companion.
Vincke goes on to reveal some other plans for the game that eventually had to be scrapped, including several locations. Githyanki queen Vlaakith's palace, the Gith Astral Plane, and Candlekeep were all intended to be explorable locations in Baldur's Gate 3 in an effort to try and increase the diversity of the game's environment, but had to be cut as smaller maps ended up making the game's "sense of exploration" a lot worse.
Unfortunately, we'll only be able to imagine what could have been had all of Larian's plans come to fruition. Thankfully, some of those plans haven't been discarded just yet, as Baldur's Gate 3 has been getting chunky updates ever since launch. They'll probably never add new companions or locations, but we do know more endings are on the way, and they're definitely catered towards the more bloodthirsty out there, as Vincke has explained that "evil players will be satisfied".