I'm deeply uneasy about the idea of adding 3rd party sellers. It seems like 3rd party sellers have gotten well into the realm of scammers and rip-off artists. I hardly buy from Amazon these days because of it. I doubt they'll be anywhere near as "carefully curated" as advertised. At first, maybe, not once the money starts rolling in and there's little incentive to say "no" when someone wants to sell on your platform.
Until a few months or years down the line when online sales have dropped because nobody can trust you and then you're scrambling to fix the problem but the damage is already done. Amazon is big enough that this doesn't matter as much, but with Target it will.