Throwing this in because I discovered something weird. I was trying to get filament change to work because I saw someone in the Facebook group mentioned it worked for them.
For one print, M600 actually worked and I got the prompt. However, I can't get the exact same Marlin code to replicate in a separate print.
can confirm @ncbob 's method definitely works (I sort of hacked a similar solution myself) but it's not particularly graceful shall we say :-).
Would really be nice to have M600 work properly.