Hanley - Top class winger, stand off and loose.
Lockyer - Top class Fullback and stand off.
Tomkins - Top class Fullback and stand off.
Peacock - Top class 2nd row and Prop
Fittler - Top class stand off and loose.
Platt - Top class 2nd row and Prop.
Inglis - Top class Centre and Full back.
Lyon - Top class Centre and stand off.
Barrett - Top class stand off and loose.
Lydon - Top class Centre and Fullback.
Skerrett - Top class Prop and Superman impersonator

I'll leave it there as the list would be enormous if I listed everyone. The point is those (and many more like them) excelled not only at club level but at representative level too. It's not actually that rare and when discussing positional movement at SL club level we're talking several levels below that.
I think many of the players we are watching right now will play more than one position during their careers and to a good standard too. KPP has already played centre, back row and prop and he's only at the start of his career!