I've been reading discussions on recent restrictions, Paradoxical Outcome, Workshop, etc. There has been a lot of talk on whether restricting or unrestricting some cards would promote or kill a diverse meta.
What I don't see amidst all this discussion, although I think could be helpful for promoting a diverse and healthy meta, is a consideration of semi-restricting cards, in addition to full restrictions. A semi-restricted card would be allowed as a two-of or less in a deck.
Full restriction is a bit extreme compared to non-restriction. There is quite a bit of difference in a card's influence over deck construction between when it is a 4-of and when it is a 1-of. When a deck has 4 of a certain card, that card has structural influence over the deck. When a deck has 1of a certain card, that card does not have much of an influence over the structure and feel of the deck. Some of the restricted cards, although powerful enough to break the game consistently when unrestricted, become just another card that might be useful to draw once in a while when restricted. The decks that were centered around such cards when they were unrestricted become largely useless when they are restricted.
Although it is not very fun to run into the same 'broken' deck playing the same broken cards over and over, it is always a shame to see the interesting ideas underlying these decks go to waste when their central cards become restricted. Semi-restricting certain cards to a 2-of limit judiciously could mean that such cards continue to have palpable influence over a deck, significantly more than they would as a 1-of, and importantly, enough to preserve the spirit of the deck, while reducing their likelihood of being outright anti-competition/interaction. Semi-restrictions, rather than killing decks outright like full restrictions often do, could urge players of those decks to find creative and/or subtle alternatives (through redundancies, novel facets, etc.) in response to the limitation of cards central to their decks.
Some of the cards that, in my opinion, could be semi-restricted to promote a diverse meta are: Gitaxian Probe, Ponder, Mishra's Workshop, Thorn of Amethyst, Gush, and so on. If any of these cards were semi-restricted on their own, they might become too dominant. However, if appropriate groups of conflicting and synergistic cards were semi-restricted in conjunction, we might be able to nurture a more diverse and dynamic vintage format than it is today, while sustaining a balanced meta that is critical to any healthy format.
I'd like to hear what you all think, whether you think semi-restrictions could be good/bad for the format, what cards you think could be semi-restricted, what could be done moving forward, and anything else relevant to the topic. Perhaps this has been discussed to death already (my search turned up nothing).