any chance of silver-border/acorn cards like Crow Storm getting promoted to black-border because they fit the rules?

There is a chance.

What hinders Crow Storm from being black border?

We costed it more aggressively than we normally would, but the card works just fine in the rules.

this may be a question you’ve answered before (and maybe that i’ve asked before tbh), but i saw the Crow Storm ask and wondered, is there ever a chance of an “Un-Masters” product in which a whole bunch of Un-Cards that work within the rules are reprinted in the black border?

Our bar for a product to be worth getting printed is pretty high.

Is Fluros of Myra's Marvels acorn for similar reasons as Crow Storm?

It was acorn so that it could keep partner, as I promised not to put partner on eternal-legal cards.

If Unstable had been printed with the same black-border-with-stickers technology that Unfinity used, would Crow Storm have been eternal legal?

Probably, but it might have cost more.

When Unstable came out, you said the Crow Storm was silver bordered because of its power level, rather than any rules fuzziness that usually contributes to silver bordered-ness. If it had been printed in Unfinity for the first time, how would it have meshed with the new acorn-or-not dynamic?

It would have been eternal and costed correctly for eternal formats.

Is Crow Storm also too aggressively costed for Eternal?

I believe so.

"Cards are silver border for mechanical reasons, not for flavor." I disagree. Silver border cards usually have silly flavor AND silly mechanics; both of those things are part of its identity. And not every card has both. You yourself pointed out the simple commons from Unstable that are silver bordered on silly flavor alone. Plus there's Crow Storm, which is only silver border because of power level. It seems to me that cards easily CAN be silver border for flavor reasons and not mechanics.

Black border does silly art and concepts. That’s not unique to silver border. And yes, we stretched the boundaries on a few Un-cards. For example, when Unstable was made Modern Horizons wasn’t a thing. There wasn’t a place to put a card like Crow Storm (and, yes, power level was a issue). But you’re focusing on a handful of exceptions rather than the rule. If we make a brand new card that 100% functions in black border, and we made it silver-bordered for no reason other than we put a different flavor on it, I’d be getting nasty letters about why can’t they play that card. I know this, because for certain Un-cards I get these letters, and most of those (with a few exceptions as I said above) are something we mechanically can’t/don’t do in black border. The big lesson of casual play increasing through the influx of Commander is players want access to as many of the cards we print as possible. The only time we prevent access has to be because something about the card would cause gameplay problems if allowed. Some players not liking the flavor is not a high enough bar. Every set we make has some players not liking the flavor. Kaladesh being off limits, for example, because some players think it’s too science fiction-y and not fantasy enough isn’t something we do.The good news is Magic is a game where you control your own experience because you choose what cards you want to play in your deck. If something detracts for you, you don’t have to play it. But what about your opponent? You’ve never had control over that. If they want to play Godzilla skinned version of cards for instance, even if you really don’t like it, you don’t control that. Universes Beyond isn’t changing that about the game.

Do you wish you had made Crow Storm a creature with Storm?

No, as it wouldn’t have worked at the time.

Could we ever see a black border version of Crow Storm?

Unlikely at that cost. Being silver border let us push it a little.