As an inveterate planner and analyzer, I still looooove the idea of this sort of thing (regardless of whether it's still A Thing or not). But I find it really difficult to apply to my own way of getting dressed. I don't really favor column-of-color or suit-esque (matching bottoms and topper) looks, so a "mix-and-match" capsule will always be less mix-and-match for me in practice than in theory.
For example I too love The Vivienne Files, but I often find myself scrolling through her posts of a dozen or more outfits from a handful of clothes and thinking: I would only actually *want* to wear one or two of those looks.
I am slowly building an understanding of "my version of" a mix-and-match capsule but it's harder to work out, and harder to achieve, than it looks!
I think that whatever system you come up with, you have to make sure that when you edit things out of your capsule you replace like with like. That might be as specific as replacing one pair of mid-wash boyfriend jeans with another, or as general as making sure that you always have a pair of light neutral pants that can be worn with cropped sweaters (for example). And when expanding your capsule, thinking similarly about expanding like with like. Maybe you wear a lot of striped sweaters in the spring, and you realize that since you mostly wear them with neutral pants you could expand your stable of classic Breton stripes with a red striped sweater. Or maybe you want to experiment with a new pattern so you add a blue paisley sweater in a similar cut to your striped ones. Maybe it comes back to that idea of varying an item in one dimension only?
