Dump1090 from Mutability (as per obj)shows helicopters with a little helicopter Icon. I see the NYPD Helicopter every day. They likely use it for TCAS as they fly is some very busy airspace.
In the U.S., I think only ATP Helicopters require mode S or ADS-B at the moment.
I live in Brooklyn, NY, with helicopters taking off maybe 100 times a day at the Wall St/Downtown Heliport. Mostly for tourists, a few DHL courriers and a few S76 (Loud and twin engines).
In 2020, when ADS-B is mandatory in the U.S. for most controlled airspace, you will see a lot more.
I expect many will opt for the 978Mhz UAT as it provides for weather and other features but it probably will depend on the cost. 978UAT will satisfy the requirement of aircraft that don’t go above FL180 (Class A Airspace in the U.S.). Most Helicopters don’t go anywhere near FL180.
UAT 978 is only used in the U.S.(at the moment) so aircraft that travel to Canada or Mexico may go for the 1090ES setup.
Flight aware makes money from Commercial flights. They may add these features to their code, however, as they won’t make money from it, I don’t expect too much development.
I have dump978 running and haven’t seen a UAT978 hit in a few days(only ground station messages)
I expect to see a lot more traffic by 2020.