Hey Terje,
good idea, good design and nice pictures again!
One thougt: I think people who like such milling motors would appreciate it very much if there was a motor mount for the milling motors with quick tool change, like Mafell FM 1000 WS, the Mafell FM 1000 PV WS and the AMB milling motors with tool change.
You can see one in the video of the someone who managed to design and make a dust boot that is controlled independently from the milling motor
By the way, the Mafell FM 1000 PV-WS and FM 1000 PV ER (with ER collet) have a speed control port that you could control via a PWM converter by the Onefinity controller. You could control the rotational speed using G-code commands from the g-code program like you would do with a spindle.