Would be nice, but I imagine that Samsung would both need to actually be impacted in an meaningful way with their store, and find some way to prevent Play Services (which they have to meet requirements to be able to load on their devices) from just nope-ing non-registered apps. Both of which I seriously doubt would happen.

They have already been working pretty close with Google on things that removed their actual Tizen OS from stuff like their watches in favor of merging their code into Android Wear OS. Would also guess that they might just work something out to either force apps on their store to be signed by Samsung and cleared by Google. Or that they just require apps on their store to only be listed after registering with Google. Not like Samsung really cares about supporting side-loading if the apps aren't in their (or Google's) store.

Sadly I think only a OEM like Samsung would have the massive levels of hardware sales and money for making a real fight against Google. F-Droid and other alt-stores or projects lack both and are easy to ignore. If Samsung were to be actually concerned about this, then I think we would have already seen them filing lawsuits and pushing posts/news articles condemning Google's plans like F-Droid keeps doing (aside from lawsuits due to money).