I had my interview last week, but I abandoned my employment-based application in favour of one sponsored by my naturalised wife; if you're trying to detect phoney marriages then even a cursory interview is a better idea than no interview at all.
Given that we turned up with all the proper paperwork and good documentary evidence of intertwined finances, living arrangements, etc, in the event it was mostly trivia questions about each other, amicably put. Then a few minutes on British television while the interviewing agent processed his paperwork. A very relaxed environment.
Having watched my field office's processing dates slowly slip over the year since I filed, I can easily believe that people are being moved around or are spending more time on things than they were: the interview was a month later than my lawyer's most pessimistic estimate at the time of filing, and four months later than her most optimistic. Which sadly means absolutely no way I can be a citizen in time for the 2020 election — at the theoretical speediest a green card by marriage takes three years to convert to citizenship, which is already too late, and there are two further processing queues to proceed through that I dare imagine will add further delay.
Ironically, the main benefit of becoming a citizen of the United States would be that we could move back to Europe. Otherwise we'll find ourselves in a spooky perpetual twilight where access to the US, which is now her only country of citizenship, is in theory always available to me, but subject to the same arbitrary bureaucracy but without the advantage of presence.