Hi Fouga,
I imagine the PC 21 will only replace the F5 in its LIFT role as the F5s are pretty much demobbed from the AD role by the F18s. Pilatus have designed this aircraft to be the only one available that can complete all training aspects from Ab Initio all the way up to LIFT. It will be interesting to see if the Swiss replace their PC7s, PC9s and F5s with the PC21.
ST