The brief is to make the feed look and feel more like X, cleaner and more monochromatic. So here is the same feed rendered five ways, every theme just a swap of design tokens over one component. Compare them side by side, then flip the live canvas between all five and read what each one trades.
All five at once
One post, one set of tokens swapped per column. The fastest way to judge cleanliness is to see them adjacent, so the differences in color, density, and contrast are obvious.
Live canvas · switch the whole feed
Tap a version. The entire feed column re-skins instantly, no reload, because the only thing changing is the token set.
The five, explained
My read
Lights Out stays the default, it is what people already know as X. I would ship Editorial as the reading mode for long posts and Articles, because the extra air and contrast is where the SpaceX-card cleanliness lives. Monochrome is the bet worth testing: stripping blue down to links-only makes the whole feed calmer and more premium, which is the exact direction of making it stop looking like Twitter. Dim and Compact are preferences to expose, not defaults.