Bronx
Much of the discussion revolves around icing! I personally having seen another pilots report do not consider this was an issue.
2000 feet and you were in the blue that day so we are talking about early morning lifting fog and mist! Probably isolated by river versus cold building syndrome.
For the most part he was flying VFR albeit minimal VMC conditions and his main exposure to visible moisture would have been scud running the odd patch of lower cloud.
Hardly an icing situation! A declared problem and request for IFR would have had him in clear air on top in minutes.
Hence I do not think he even thought he had a problem until the impact with the Crane arm.
I do not know a lot about Flarm but from more knowing posters here maybe there could be an application developed to identify threats in City situations and even an insistence for Helicopters flying these routes to be equipt.
Flarm appears to be relatively cheap and nowadays we are forced to carry very expensive equipment to save us from ourselves.