With the AEC topology on main, the following endpoints get listed.
i see the following o/p:
rex-rev1 ~ # arecord -l
**** List of CAPTURE Hardware Devices ****
card 0: sofrt5682 [sof-rt5682], device 0: Headset () []
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: sofrt5682 [sof-rt5682], device 2: Bluetooth () []
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: sofrt5682 [sof-rt5682], device 27: DMIC0 RTC AEC () []
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: sofrt5682 [sof-rt5682], device 28: DMIC0 RTC AEC NS () []
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: sofrt5682 [sof-rt5682], device 29: EchoRef () []
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: sofrt5682 [sof-rt5682], device 99: DMIC Raw () []
Subdevices: 1/1
Subdevice #0: subdevice #0
rex-rev1 ~ #

This sequence doesnt work:
1)start speaker playback
2)start dmic capture: arecord -Dhw:0,27 /tmp/tmp.wav -c4 -r48000 -fs32_le -vv

there is a strong dependency on echo reference endpoint to be started.
While this works:
1)start speaker playback
2)start echo ref capture
3)start dmic capture: arecord -Dhw:0,27 /tmp/tmp.wav -c4 -r48000 -fs32_le -vv.

There is no need for the echo reference endpoint to be opened from the user space, while speaker playback the data can be fed to AEC without the FE.Kind of hostless stream.