Please write in to sales@carbide3d.com — I know we have an 80mm diameter spindle in development for the SO5 Pro, and I’m hopeful that it will be 110/220V auto-switching (or have a manual switch?)
I do have to admit that I use a European 220V spindle on one of my machines — a Mafell FM 1000 WS:
https://produkte.mafell.de/develope/en/mortising/milling-motor/milling-motor-fm-1000-pv-ws
it was something of an indulgence (I was doing so many test cuts at the time it felt as if I was spending more time wrenching than the machine was cutting), but has worked out surprisingly well — I’m still debating about making an adapter plate for my SO5:
it works well, despite the nuisance of needing a 110–220V step-up transformer.
If you’re interested, I could push that up the priority stack.