This is all "just for fun," but then given the often vitriolic postings here (quite unfortunate and laborious to sift through, btw), why not add a bit of levity?
I'm curious with this wealth of Vintage expertise on TMD to see what cards you all might design/propose specifically with an aim towards opening up the metagame. My sense is that virtually everyone here is at least somewhat disappointed with the Mentor vs. Ravager Shops dominance, and much has been opined in terms of recent and future restrictions. I also know that most of us would favor new printings over restrictions/bannings in terms of regulating said metagame. Not that it probably "matters" in the grand scheme, but to at least inject a fun exercise here I wanted to ask what card/cards might you propose to diversify the format? You can consider the effects on Standard, Modern, etc. OR NOT, but what dynamic(s) would you find helpful in cultivating realistically competitive decks outside the more popular motifs? I'll throw out a couple of silly suggestions just to get the ball rolling:
T: Add one mana of any color to your mana pool. This mana may only be used to cast enchantment spells, and any spell cast with mana from this land cannot be countered.
Creature - Merfolk UU 2/1
While ___ is in play each opponent cannot cast more than one spell each turn.
As MTG experts I would assume there are some extremely creative minds on this site. What strategies/themes intrigue you, and specifically what new card designs might you propose to make them more viable in Vintage? Green Stompy? Infect? Merfolk? Elves? Death & Taxes? Mill? Infinite Turns? Land Destruction? Landstill? Etc.?