> We already have plenty of techniques that are fast enough for classic UI rendering. There is no conceivable bottleneck for the kind of stuff that is on your screen right now.

I disagree, you either have the old object-oriented toolkits, which are fast enough but very unpleasant to, or the new reactive frameworks, that offers much better developer ergonomics (and that's why pretty much everybody uses them right now) but have pathological performance characteristics and requires lots of additional work to be fast enough when the number of items on screen is high enough.

By the way you are missing the forest (Xilem) for the tree (Vello) here: the foundational work Raph has been doing isn't just a 2D renderer (Vello), this is just a small piece in a bigger UI toolkit (Xilem) that is aimed at addressing the problem I mention above.

Xilem originally started using the native libraries for 2D rendering (through a piet wrapper he discusses quickly in the video) but ended up being disappointed and switched to making his own, but that's just one piece of the puzzle. The end goal is a fact reactive UI framework.