I wonder if they are going to change some banned mechanics in some competitive metagames. For example, the Sleep Clause could be abandoned if the Drowsy mechanic is introduced instead.
But what about other clauses. Let's talk about banned abilities like Shadow Tag / Arena Trap or Moody. How Gamefreak could update those abilities to be unbanned, while remaining interesting?
For Shadow Tag / Arena Trap, I think it is more the strategy around setting yourself up against a Pokémon that cannot do anything or the non-fun Struggle game, and less the revenge-killing. One way to change the ability is to either prevent the Pokémon from switching out / flee on the first turn only, or the ability could act like the deleted "Pursuit" move: When the opposing Pokémon is switching out, your Pokémon uses its move immediately before it is switched out.
Wobbuffet would probably need a new ability if the "Pursuit" variant is chosen.
For Moody, I think the ability has 2-3 problems. It is both unreliable and yet, potentially too powerful, while enacting non-fun stalling game in order to gain those stats. I think Moody should change in behavior. Instead of decreasing a stat's stage at random, it should decrease the one that raised the last turn. If you had +2 Speed last turn, you will have -1 Speed next turn. It means that a same stat cannot raise two turns in a row (getting +2 Attack and -1 Attack would be weird), and also means Moody will have no stat drop on the first turn (since no stat raised last turn). This would prevent both being too unlucky (having 2 or 3 Defense drop in a row), or too lucky (gaining only Speed / Attack boost while losing Special Attack on a physical sweeper).
If the ability is still too powerful after that, I don't really know what to do. Either remove the Speed increase from the ability (it used to increase Evasion and Accuracy), or worst, give a -2 stage drop instead of -1 (meaning you will have only +2 stage at once from the ability).