This would be useful for us as well.
We have 3d printers, chromecasts, firesticks, streaming cameras, and other devices that all rely on mDNS.
It would be extremly useful to be able to mDNS forward these discovery requests to other vlans / wLANs.
Or at the very least add some of these other mDNS strings.
I would also be useful to supress mDNS on a VLAN, like you can do with cisco WLC.
IE: I want to be able to control what mDNS wLAN users can share with other wLAN users.
Like I don't want them to be able to share air printers.
while also, at the same time, being able to share air printers from a wired vlan.