@neo_altoid But that's not really argument for gush's restriction. Only because most blue decks run the same draw spells doesn't mean this draw spell needs to be restricted. For example, you could make the same argument about preordain. How many true non-preordain decks were there? this is the old "diversity in draw engines" argument that has been made over and over again. Put it to rest. Different Gush decks play very differently. Even Grixis pyromancer and mentor (two TX token strategies) play(ed) differently.
So, after the restriction, we can see that gush is not necessary for the TurboXerox engine to dominate. Even restricting every 1-mana cantrip wouldn't hurt it. I'd say the problem is that there is a finisher that is easier to cast than tinker (no artifact in play needed), requires less investment (sacrificing an artifact, running a dead card), is harder to deal with, and kills about as quickly. The only requirement said finisher has is "play lots of spells, doesn't matter what the effect says on the card."
On the other hand, some decks conceptually rely on 4 gush to work, such as doomsday for example, or any form of gushbond decks (which have been outclassed a long time ago). Not only have these decks been killed by the restriction of gush, the very POSSIBILITY of "innovating" with gush has been removed! that's what wappla means by removing bricks I think.
(Grixis pyromancer has been killed by the printing of walking ballista though, and then killed again by the restriction of probe; DPS also has been killed by restricting probe). The problem with probe is the same: the spell is only problematic when it summons a seeker of the way.
Long story short:
restrict mentor. unrestrict gush OR fastbond. unrestrict probe. unrestrict memory jar. unrestrict yawgmoth's bargain.
see what happens. if the main problem in the metagame continues to exist (I think it has been well defined that at the moment there is a two deck metagame with MUD and TX: mentor), try more things: One possibility:
restrict misstep and sphere. unrestrict chalice of the void.
Restricting misstep would make real 1cc-counters better, like REB (opening up the possibility of painters), spell pierce + snare, as well as making hand disruption, rituals and 1cc-creatures better.
Restriction of sphere is not a very obvious one, but I think it has some merits, because sphere is unconditional (removes deckbuilding options to play around it) and is only usable for workshop decks. While creature decks don't have problems with thorn, they do with sphere.
Chalice on the other hand is a card that can be used in or even enables a variety of decks (MUD, Blue moon, some baral-2cc-mono-U-control, could make eldrazi and other critter decks stronger, a white deck with chalice and chalice man, etc.) and is very effective against the cantrip menace, (unlike misstep, which forces blue decks to run their own missteps to counter the opponents missteps that countered the misstep which add more dead draws against MUD). Also, chalice is nullified by cavern of souls. It would also give all the decks an option against PO decks, while being relatively easy to answer for these decks set on any number via engineered explosives (with the help of strip/library/sol ring/mana vault/monolith mana). I'd only unrestrict chalice if at the same time restricting sphere though!
Also: the workshop: Magic players tend to forget that mishra's workshop has a weakness: All permanents in a workshop deck have the artifact type. one hurkyl's (or anything else) to rule them all. Eldrazi are already harder to answer, because their card types vary (but is worse as a deck). And at the same time, the taxing deck is important to have in vintage, to prevent t1 glass cannons and TX strategies from totally dominating. The goal should be how to make shop decks a little worse against Non-greedy TX/combo decks.
All in all, I'd look for restrictions and unrestrictions which open up possibilities of deckbuilding and foster variety, without destroying archetypes like workshop or gush decks.