4Greens
Trouble is ( as I understand it, and I'm definitely ready to be corrected) "traditional" ADS-B won't really help you find your hypothetical crashed aircraft in the oceanic case...for dare I say obvious reasons?
ADS-C might help but even then the aircraft can travel a long way between reports, though there is the provision for the automatic alerting of ATC if certain parameters are breached (e.g. Altitude deviation).
Lots of movement re ADSB in Australia.
Most of Aussie ADS these days in the upper airspace seems to be ADS-C, even overland.