We already have an “anything goes” card design thread. I’d like to start a similar thread that is a bit more focused. I’d like for this thread to be for cards that, if published, would likely result in an improved vintage metagame and improved vintage gameplay.
Improving the vintage metagame means that the card should either reduce the effectiveness of current dominant strategies, or increase the effectiveness of current second-tier strategies. A good litmus test here is to see which cards are a hot discussion for potential restriction. But the effect should not be too violent (e.g., a card that says “I win if you have Mishra’s Workshop in play”).
Improving vintage gameplay means that the card improves the interactivity and skill-level of the game as a whole. The publishing of the card should increase the likelihood that the more skilled player wins. This can be achieved either by designing a card which requires skill to play with/against, or by designing a card which neuters the effect of existing skill-reducing cards. To illustrate, highly skilled players are better able to reason about hidden information, so cards like Gitaxian Probe which reduce hidden information reduce the skill advantage, making it a poor design choice. A card that somehow makes Gitaxian Probe less playable would be a good entry for this thread by virtue of neutering a skill-reducing card.
To put further constraints on design, the card should not introduce power creep. Ideally, the card is not playable in Standard. This makes it more likely that Wizards might adopt some of the popular proposals without worrying about the effect of the card on more important formats.