A Zynq-7000S might be WAY overkill for this project, but I mean, I'm going for flexibility with this, so I'll just add some high-speed mezzanine connectors for daughter boards and call it good.
The question then is what would the daughter board need? I'm thinking I could just shove power, ground, a dozen or so GPIO lanes up it? I don't think it'd need anything else.
I don't plan on selling this, so why on earth am I thinking about user-made mezzanine boards.....
We are a cute and loving international community Ｏ(≧▽≦)Ｏ !