Over the past few weeks I've been working on fractional scaling for niri. A simple implementation took about a day, but to do it *properly* I had to refactor the entire layout code to work in floating-point.
The result is well worth it though. Borders, gaps and windows are always physical-pixel aligned, and not restricted to integer logical pixel positions. There's no blur or position-dependent +-1 px jank. Fractional-scale-aware clients remain crisp at any scale.
So it turns out that changing PipeWire screencast stream resolution on the fly is actually not that hard! Which is great news because it's required (or at least very desirable) for implementing window screencasting.