OFC, I'm assuming a utopic world here. There's no incentive for neither Youtube nor the creator to do this, as opposed to simply linking more of their own stuff or whatever is ad friendly.
Maybe an author's hilight section and then an "other replies" that's more open.
Even when it was available I've only ever seen a few cases of it working well. One prominent one was an educational YouTuber (Veritasium) asking users to post video replies with solutions to a physics puzzle/experiment that he was doing. Besides that, the feature was not used by creators and so spam videos and response girls were rampant in the video replies to most popular YouTubers.
If memory serves, that was ultimately what got the feature on its way out.