FYI: Chains of Mephistopheles with modern templating does fit on a card. That doesn't make the card reprintable or the effect any easier for non-judges to grok, but it would physically fit on a card.

FYI

"It’s all a matter of perspective. Commander has rules that don’t exist in most formats." I think this isn't a fair comparison. If you try to play Frankie Peanuts as your Commander in a game of Magic, you'd see very quickly why a lot of players don't like it when cards don't have clear and official rules. When you play those cards with black bordered cards in constructed Magic it creates uncertainty and confusion. PLEASE don't put silver bordered cards in black bordered products.

Frankie Peanuts has caused less rules confusion than Chains of Mephistopheles or Humility. The idea that black border Magic is different because its cards never cause gameplay confusion is simply untrue.

In the case of Oubliette or something like Chains of Mephistopheles where the wording of the card literally can't fit on a modern magic card... have you have considered creating an evergreen keyword that just means, "refer to the oracle text" or just "read the rules somewhere other than the card".

We haven’t crossed that line yet. Well, at least in black border.

What does Chains of Mephistopheles do?

Confuse players. : ) It makes you discard cards whenever you draw cards, but in a complicated way.