I've read everything in this thread and after seeing that a few people seem to think that only @Smmenen wants Gush to stay unrestricted, I decided to submit a rare post.
I enjoy Vintage as it is right now. I enjoy playing with Gush. I enjoy playing Gush mirrors and I enjoy playing against the other decks which I typically encounter in the format whilst playing with Gush decks. My experience of Gush is that it promotes a pattern of play which is more interactive and (subsequently) typically slower than games in other formats such as Legacy.
One of the things that I especially enjoy about Vintage is that it is a format where attrition strategies are less prevalent. Modern, for example, is a format where Black-Green decks are king because one mana hand disruption spells are the only real universal interaction which exists in the format. Those kinds of strategies exist in Legacy too, but they don't really exist in the same way in Vintage. I like that. I like that the format is different in this way.
Another thing which I really enjoy about Vintage is that the format has very high power peaks. My thinking is as follows: in a format where there is a power peak, there will always be a playability vacuum as a result. In Legacy, no one plays Condemn or Oust as one mana creature removal in White because Swords to Plowshares exists. I like that Vintage is a format with relatively few power peaks, and that those power peaks are very high. It creates an enemy to fight, rather than having the sea of mediocrity which exists in Modern, for example.
I am reluctant to post and argue my position too fervently for several reasons. One of those reasons is that I don't believe my voice has the capacity or carries the weight to make a difference at all. Another reason is that I am acutely aware of the fact that my opinions are not perfectly informed - they're shaped by my experiences and preferences. As such, I know that my opinions are enormously subjective and so I don't believe they are worth anything to anyone else. Which I think is totally fine.
With respect to a change in the format, I have said on Facebook that I believe that part of the problem with Vintage right now is that people seem to be unhappy with the pattern of play that Monastery Mentor promotes. I mentioned that people dislike that Mentor is mostly immune to removal and that it is so powerful while requiring no synergy in order to be both an efficient defensive or offensive tool.
I suggested that if people are dissatisfied by the pattern of play which Monastery Mentor promotes, then restricting Mentor rather than anything else would be preferable - partially because cards like Preordain, Gitaxian Probe and Gush go into other strategies which people find less infuriating to fight (like Storm, Oath of Druids or Fastbond based combo decks).
Another thing which leads me to believe that perhaps Mentor is the card to restrict is that the Gush decks we see today are very powerful without maximising the power of Gush. If I'm not mistaken, Steve made this point previously, saying that Gush decks play more land and often don't even play four copies of Gush. It is my opinion that the efficiency of Monastery Mentor is an enormous chunk of the reason that control decks can exist in this manner. By providing a win condition which is highly challenging to efficiently interact with while having such a low opportunity cost, people can play Gush decks in a way which I would imagine wouldn't be possible without Mentor.
There are many other factors which influence contemporary deckbuilding: the printing of the Eldrazi and the restriction of Lodestone Golem has resulted in a scenario where many players are incentivised to play Swords to Plowshares as removal instead of Lightning Bolt, the printing of the Delve spells and Dack Fayden has also had a tremendous impact on the format, Containment Priest's printing has changed how we typically fight graveyard or Oath strategies and Paradoxical Outcome's printing has drastically increased the stock of Stony Silence. These things all work in unison such that isolating their impact may not be possible.
I don't know what the best thing is to do going forwards, but I can say that I enjoy Vintage with Gush. I really love that Vintage is a format which massively rewards skill and provides players with agency which I don't think we get in other formats. Gush is a part of that for me.
It is very possible that I'm wrong and I will continue to read the opinions of others and challenge myself to consider things from their point of view.