This is only another attention-grabbing exercise from Elon, so I don't want to give it any air.

But to clarify, when Elon Musk says this:

Block is going to be deleted as a "feature", except for DMs
That's actually not going to happen.

Why?
 
Because it would violate both the Apple and Google Play Store guidelines, which would then render X ineligible to be hosted on either, effectively killing the app.
 
Which guidelines?
You might be able to argue that the wording of the Apple policy is somewhat vague, as it doesn't at least specify that individual users must be able to block users, and the service shouldn't. But if there's any ambiguity at all in the wording of the Apple policy, there certainly isn't any in the Play Store listing.

Of course, Elon has seemingly been allowed to bend such rules in the past, on naming conventions for apps, and on content moderation, for example. So he may, possibly be able to manipulate them again, though this really seems like a step too far, which neither Apple nor Google would be able to allow.

Why would Elon even want to remove blocks?

Because it reduces ad impressions, by limiting content exposure. There really isn't much other logic, though Elon has also complained in the past that supporting block lists is problematic for X's systems.
Maybe that's the motivation, maybe not. It's not exactly clear.
X CEO Linda Yaccarino has since gone into damage control, in an attempt to soften Elon's statement.
Which basically eliminates any avenue of making this a possibility given the rules stated in the App Store.

So this is more of Elon firing off takes without thinking, which helps to get him more attention and maybe X too.

But no this isn't going to happen in reality.

And yet here I am, playing along and feeding into the Musk media machine.