What if there were special relics that’s only on certain maps. That produces all four resources. It’s not present on most maps. It’s only present on new maps that feature this new relic. However, when you host non-ranked games, you still have the option of allowing this relic to exist on normal maps.
A Grand Relic or something, they called.
The idea of a relic is that it represents a holy, well, relic, and the gold trickle comes from the pilgrims who foolishly waste their time looking at it, and pay for the privilege. 
Also, trade workshops are kind of what you are talking about. I know they aren’t relics, but they are the closest map specific thing we have right now. I think probably not though overall. Unless it became a new tech like the AoE4 Tithe Barnes that let relics generate a trickle of more/all res, but at an even slower rate then they do with gold.