The ER-11 collet on the VFD spindle maxes out at 8mm.
You’d need an ER-16 or ER-20 collet system to go larger — we use ER-20 on our Shapeoko HDM, and we have an 80mm mount and matching spindle in development for the SO5 Pro, but no word on specifics or availability (check in w/ the folks in Sales) unless @Luke can share something?
That said, see:
which while not condoned or recommended or supported, does show what one can do with tooling at the end of a long shaft if one has feeds and speeds dialed in and if the tooling is suitably balanced (says the guy who had to all-but tear down his SO5 after an ill-balanced tool caused things to shake so badly bolts started to vibrate free) and if one keeps cutting forces to w/in what the mechanism will allow.