Nope no GPS. I'm not even joking either -- it's navaid to navaid. Navigation to IFR waypoints is done by old school point to point radial/range from a known navigation aid by visualising your location on the HSI. The tolerance on an instrument rating test to be checked out is 2nm for one of these.
Yes they spend 80% of time in ESL/PEA airspace but (a) Other IFR aircraft also transit, (b) Roulettes fly all across the country and sometimes international island hopping. (c) it's very common to do IFR Nav trainers to Essendon/Perth/Albury/Wagga/Tamworth/Geraldton/Learmonth/Albany etc.
Worse, they have a single generator and poor batteries. Lots of generator fails recently. If you're in IMC there's about 10mins to turn off some stuff, get visual and consider extending the gear to check 3 wheels before complete loss of electrical power, no artificial horizon and ejecting.
At least without ADSB, ATC won't be able to see the lack of RNP compliance!
Yes there's a warehouse full of GPS's but due to complex issues involving training downtime and contract issues for fitment, were only fitted to a couple of aircraft at ARDU.
Also, the pc9 transponder is a small square one (around 2.5"). I could be wrong, but I don't know of any small ADSB transponders with inbuilt TSO146 GPS (or whatever the inbuilt spec is).
So no, I highly doubt you'll see ADSB on any PC9's any time soon Dick.