A month ago i tried to get the new WLAN mesh running with my Fritz!Box 7490 and Fritz!Powerline 546E.
Some days ago AVM release a new firmware for the 546E:
But even with the new firmware the powerline adapter does show up with the "mesh symbol" inside the home network overview:
I am wondering, if the WLAN mesh only works by using the powerline connectivity. AVM support pages show up the following advisory:
Inside the networking overview my 546E is registered in this way:
Hopefully the next update may fix this.