I like the ideas! Here are some of my own:
1. 2x Protagonist - I think the 'next generation' of RPGs like CDPR makes, Starfield makes, etc. are for someone to master origin stories and starting as different types of people or just different people in general. I'll use Geralt and Yennefer as examples so that it is easier to understand.
But I think it would be a cool concept to be able to play the story of The Witcher 3 from Geralt's perspective. You fight like a Witcher, solve problems like a Witcher, people treat you like a Witcher... so on so forth.
But then you could also play as Yennefer from the start of the game if you choose her. You fight using magic, solve problems in magical ways, people treat you like a sorceress, etc.
Your stories would intertwine. There would be 'default' and 'canon' Yennefer actions and Geralt actions when they interact and things like that. But your plays of each character would offer unique interactions and choices that could impact the world, the other main character and the ending(s) of the game.
You could start at different points in the world, major characters and plot points could play out differently, there could be different endings, etc.
Is this too much work for a developer? I don't know - because I am not one. If it is, then I guess the idea is a terrible one. But it seems like the Resident Evil games have managed to do this once or twice. Divinity: Original Sin 2 dabbled into this and Baldur's Gate 3 is kind of getting into it with their origin character system. But I think this could be insanely cool in some of these big RPGs... while offering both unique experiences and a high level of replay-ability.
2. Swords, but different - Witchers seem synonymous with swords and I think keeping them around as the primary weapons are great. But it would be neat if there were long/heavy swords that offered slower, big higher damage attack. Medium sized swords that offered a base style of combat. Katana type swords that maybe offered a quicker type of slashing but could stack bleed effects. Short swords that are almost like daggers that offer fast attacks and potentially benefit sneaking type mechanics.
3. Morality System - I say this only if it has a genuine impact and is done right. I thought Mass Effect did a decent job of it and the original Fallout games had some neat stuff with it. But make certain actions have consequences that are long lasting based on if they were good, bad or indifferent. I imagine Geralt is gone and we are going to play as a custom character, so this seems far more important.
