I believe ADSB is fantastic but I do not know of the safety issue that is being addressed with the $100 million subsidy.
As far as I know there has never been an accident between an IFR and a VFR aircraft in our history and if that is a measurable risk it is well served by proven TCAS and a transponder together with radio and dare I say it, also looking out.
There is no ADSB "in" unit anywhere in the world that gives a Resolution Advisory - so why not at least use proven TCAS/Transponder equipment first.
That is unless it is imperative the VFR aircraft appears on the AsA screen so some form of "service" and charge can be given.