Not sure if this is meant seriously but ... I'd say there would be (to my mind at least) massive problems with "prevalence" and "interesting & informative".
As you note there are loads of CCTVs in London, and none of them are in the least bit interesting. Why one earth would anyone want to a) photograph or b) visit one of these?
There was even one in my back garden last year (I was observing the urban foxes).
I suspect the writer of the following comment did not mean for it to be taken literally.
"I wonder what they will do as photographing CCTV cameras becomes the next hot photography fad? If something as inane as train-spotting can catch on, surely a whole new subculture that rotates around documenting and collecting Big Brother paraphernalia could emerge."
They were daring the nerds out there to be nerdy enough as to photograph CCTV cameras. Are we up for it?