I arrived back at Heathrow this evening at 8:45 PM, Terminal 3. My plane was an hour early.
The regular passport control line snaked through the entire immigration hall, up the ramp and almost as far back as the nearest gate.
Fortunately, I could use the e-gates and from the time I entered the immigration hall until the time I cleared the gates was about 2 minutes.
If ETIAS means I can use the electronic gates at more airports, bring it on.