Thanks @The-Atog-Lord for a thought provoking piece.
The thing that struck me most was what @chubbyrain said:
I would also argue that Gush really isn't weakened relative to the field. It still has incredible synergy with Dack Fayden, JVP, the delve spells, JTMS, Mentor, Pyromancer, Managorger Hydra, Nahiri, etc... You still end up with virtually all Blue decks adopting the same Gush Engine, just with other ways of extracting value from the card rather than a tiny manabase.
The current state of Vintage reminds of a variant my uncle and I used to play similar to today's Canadian Highlander where each card had a point value. Unlike Canadian Highlander you could play multiples - even Type 1 restricted cards - provided the overall number of points was within the limit.
As time went and more cards were printed it became impossible to keep the power level of two card combos in check without assigning absurd point values to cards which in isolation did nothing (e.g. Illusions and/or Donate). This meant they couldn't be used in other decks either. The fix was to eventually assign points to two card combos, but it was the beginning of the end of what had been an enjoyable format until then, and I'm determined to give Canadian Highlander a try at some point.
Now in Vintage there is no cap on the number of restricted cards you can have in your deck (as long as you only have one of each :) ). As long as Wizards continue to print cards that have synergy with the other cards in the Tier 1 decks particularly TX/Shops they will push the power level of these decks up.
I believe @Smmenen when he says that gush was not a problem pre-Khans. But I think the genie is now out of the bottle. And while it would be nice to restrict pairs of cards (i.e. you can play with only one copy of A & B (X)OR 4 copies of A X(OR) 4 copies of B) that would be simply be a different format that isn't Vintage.
Eventually synergy becomes "too good" (and I accept some people such as @brianpk80 describe this in a qualitative way and others want to see quantitative hard data based on tournament results to assess this). But if Wizard's agree something needs to be done the only tool which they have available is to restrict one of the cards that fuels the engine (or the win con).
Unless Wizard's stop printing cards that fuel these engines it seems there is only one place Vintage will end up - an endless string of restrictions. Sadly I don't see this increasing diversity if a deck of singletons is still Tier 1. Though since you'll be playing quasi-highlander maybe gameplay will be a bit more diverse and people will complain less.