By default every poke would breed into one region (probably kanto by default (configgable of course)). You'd use the infuser to infuse a bucket of water with varying items to make different kinds of potpourri, and these would let you breed different regional variants.
For example, I breed Growlithes. By default, I'd only get normal Growlithes. If I infuse a bucket of water with fossils, I'd get Ancient Potpourri, which I'd then use on the Ranch. Now, I'd either be guaranteed or have a chance to get Hisuian Growlithes.
This would also future-proof against more regional variants as we'd simply need a new type of potpourri
There's even a perfect spot on the Ranch's current model - the blue smiley screen. It could change depending on which potpourri you use. If the potpourri only lasts for a certain period of time/number of breeds, the screen could be green then slowly lowered back to blue.
Aside from regional breeding, potpourri could be a temporary buff to breeding in a few ways. The buffs could range from simple stuff like making environmental blocks of a type more effective, to influencing the gender of the eggs, to more powerful buffs like higher shiny chance or a chance for special textures to be passed down (so we could get say a microscopic pink pidgey).
I imagine buff-type potpourri and regional potpourri should be able to combined, maybe with more powerful buffs like shiny chance taking away more uses. So say an Ancient (Hisuian) potpourri by itself could have 30 uses. I could combine it with a Fire potpourri to make Flaming Ancient potpourri with 20 uses, or with special texture potpourri to make Special Ancient potpourri with 10 uses.