On a recent flight from JFK to LHR (March 2019), there were no signs/mention of checking in hand baggage. However, I went to the check in desks upon arrival at the airport and asked (assuming the flight was full/near full) - after a bit of checking the agent was willing to do it.
Definitely not as widely promoted, but I guess if you built a case (maybe on popular routes such as JFK) this would work.