4. New Printings. This is the solution to stagnant formats that no one seems to talk about much when the subject comes up. Just like yesterday's mistakes are tomorrow's Vintage decks, today's bugbears are tomorrow's unplayable garbage. We have already seen Wizards take a step in the direction of making very versatile and powerful answers to Mentor in the form of Leovold. What if we get Dread of Night stapled to a hate bear that does something else relevant? What if we had some card that finally, FINALLY ended the reign of Horizontal Growth once and for all -- say, something that made the opponent's spells cost more for each token they controlled, or something like that?
While I totally agree with preferring new printings to restriction, I think it'd be pretty tough for Wizards to "target" new printings at solving the problems of any format, other than Standard. I think it happens on accident when a new card does warp or add something to a non-rotating format because WotC either doesn't think a certain mechanic will end up making the cut in eternal, or they just don't consider the entirety of Magic when they innovate cards (to many a brewer's delight). I personally think it would suck to have a card like what you describe printed, Wizards would be addressing the problem with a "play it or beat it" mindset, which would make me super uncomfortable as a Vintage player, not to mention it's far less expensive from their perspective to restrict a card than to print a new card.
Good new printings usually emerge as cards that end up propping up various other archetypes that as a side effect, hurt the big bad deck. Not saying that Shops is hurting right now (quite the opposite), but if Mentor is the target of our discussion then cards like Fleetwheel Cruiser or Walking Ballista are "good new printings" because they help boost the competition. (I personally like it best when WotC makes a mistake and prints a 2-card combo with some obscure Tempest card I haven't seen in a deck since 1997, but that's rare ) Thinking in those terms it would be very difficult to see an "accidental" new printing resolving the Mentor issue, the "other" deck has 3-5 new cards in the past year to combat Mentor and boost its own strategies, but Mentor remains a problem.
Since this discussion has gone into minutiae, this isn't really necessary, but I felt like I should bleep in.
I've been saying this for a bit... Gush wasn't completely busted until we started using a 3CMC "gro-wide" creature as a 4 of. Gush in any other creature-based shell was reasonable, and I can't believe I'm saying this because Pyromancer Gush was/is very annoying and boring to play against, but I'd rather deal with U/B/R Delver with a healthy dose of Elemental tokens flashing back Cabal Therapies than deal with any deck that uses Mentor. Mentor is oppressive, uninteresting, and unfun; taking out tokens is key to surviving the fight of both Pyro and Mentor, but Monk tokens are far more resilient and oppressive than Elemental tokens, and they are generated and pumped by enchantments and artifacts... A much different beast altogether.
Point being that if you don't like Gush decks mentally ruling the metagame, restricting the card that profits off of it the most is probably a good way to go.
Some questions I think need to be asked, and I rhetorically answer them because, why not.
If Gush were the real issue, wouldn't (at least) one other Gush-based deck be a runner-up in the meta, and be an obvious successor to Mentor, should Monastery Mentor be restricted?
Considering the other two Gush decks are at 3% and 4% of the meta (Pyro Delver and Nahiri respectively), they both don't add up to half of the numbers Gush Mentor has in the meta (23% of decks as of 4/10/17), even adding the 1% from Gush/Bond. I assume the percentage of Pyro Delver would go up should Monastery Mentor be restricted, but whether or not it is good enough against new Shops variants, Eldrazi, newer Oath variants, etc, is to be seen. I personally don't think Pyromancer is nearly as good, in any way, as Monastery Mentor, and I don't think any variant of Pyromancer would emerge as the "#1 deck" should MM be restricted. And, to be quite frank, if Gush WAS the problem, wouldn't Gush/Bond really be the way to maximize and break the format, considering everyone's talking about "free spells and mana ramp" as reasons to axe Gush? Curious that Gush/bond is sitting at 1.4% of the format... Other factors certainly bear on that number, still is a bit illustrative that many of us are looking in the wrong place.
Are we certain that restricting Gush would have any effect on the metagame other than nearly wiping out that 7-8% of non-mentor Gush decks? Are we sure that Mentor wouldn't still be in top 8s by making the least effort possible to update to a world with 1 Gush?
I don't think so. Restricting Gush "hurts" Mentor like a bee-sting.
It's funny when folks mention the banning of Splinter Twin in Modern as an example of how to hit Gush... (I swear it's somewhere in the morass above)
Mentor IS Splinter Twin and Gush is Pestermite in this analogy. Splinter Twin has an analogous card that is strictly worse in Kiki Jiki (in the case of Mentor is Young Pyromancer), Twin abuses the functionally identical Pestermite and Exarch (in the case of Gush is literally any other draw spell or free artifact spell) to go broken. Imagine the DCI banning Exarch or Pestermite in order to solve the problem of Twin decks. This is essentially what would happen if the DCI restricted Gush to hit Mentor decks. I acknowledge that this is an imperfect analogy since Gush is better than Preordain to a much bigger degree than Pestermite is better than Exarch, but that is beside the point; the big baddy is Mentor.
Will restricting Gush be enough?
It would take quite a lot of restrictions in order to curb Mentor effectively, we're talking Probe, Gush, Misstep, Preordain, and maybe the next-worst cantrip as well. Eliminating 4-ofs of a single card in a Mentor list would be ineffectual at curbing Mentor unless it's Mentor. "Mentor-the-card" is the problem, its effect has been to amplify nearly every card being called for restriction in this thread and elsewhere.
I would think the goal of any restriction is to not restrict more cards, correct? Be as effective as possible in dealing with imbalances without 8-card restrictions and format micro-management? Seeing as Mentor will get along just fine without Gush and will likely need a second restriction to affect its position, not to mention the side-effect of killing gush/bond decks which are enjoyable to watch (from my perspective) and fun to play against, restricting Monastery Mentor is the most effective way to get the desired effect.
I don't want to seem combative, but it's been irritating seeing people value having the card Mentor in the format more than the card Gush. Gush has been around for such a long time, it has a history in the format for good or ill, and it's powerful but by god are we a far cry from calling Gush/Bond more "broken" than Mentor. Gush is difficult to play and is interesting, Mentor is extremely easy to play and is uninteresting.
Gush needs to be correctly analyzed regarding its power level once Mentor (which profits off far more cards than just Gush) is off the table.