CPU can be overclocked to 1,3 GHz with heatsink, 1,4 Ghz with active cooler, 1,5 GHz is unstable but probably it's a matter of time to solve it. Early benchmarks (on 32-bit OS and non-optimized software) are very promising - performance is up to, if not better (after OC) than Pi 3.
So the main question - is there a tiny chance that the projects like Zynthian (or maybe "Zynthian lite" or another DIY synth) will be available on this little SCB in the future? I know 512 MB is not much, but it's the CPU that really matters when it comes to plugins - devices like V-Machine has poor 1GHz CPU with 512 MB RAM, yet it was running many VSTi plugins perfectly.
Zero 2 W has one USB 2.0 slot - it should be enough to connect audio interface with Class Compilant compatibility. I personally have Zoom UAC2, which should be perfect for that kind of use. I don't think existing DACs for "standard" Pi will work on it.
Prices for Pi 4B skyrocketed and are a tiny bit too high, considering one can buy old notebook and make it several times more powerful when it comes to plugins/synths. But 15 bucks for headless synth? Count me in