Rate him in SL but I doubt he can cut it in the NRL.
He'd be the smallest player in the comp, by some margin. Successful little blokes are few and far between post-2000. Luke Keary has 10cm and 4kg on him according to Wikipedia stats.
He'd likely be signed by a currently low lying club willing to roll the dice. Like we saw with Tomkins, this isn't an environment to thrive. The chance of a big turnaround is slim and he'll shoulder more than his fair share of blame for losses.
The biggest question - does Theo Fages have what it takes to step up? Does his presence on the field make an average team better? From what I've seen the answers are no and no. I'm not looking at how he plays in a table topping St Helens side or in a French side flogging Scotland. I'm looking at whether he steps up for France in World Cup games or England tests. And I don't see it. I think he's France's best player, but I don't think that's good enough for the NRL at the moment.
I don't think he'll play NRL, but if he does i'd predict a handful of games early in the season then spending most of his time in reserves.