What about introducing a points system for imports.
Cant play in Superleague unless they have a certain number of points

EG
Australian International 50pts
Aust. int within last 2 seasons/S.O.O. current or within last season 30pts
Aust. int within last 3 seasons/S.O.O. within last 2 seasons 20pts

And tier it depending on ranking of said Nation, Age etc.

Stops journeyman and players looking for big pay offs at the end of thier career.
So Lockyer maybe a top tier player on paper but is penalised on points by age.

Clubs are limited to 3 players, and must contain a mixture of forwards and backs

Clubs are also rewarded for using homegrown talent:

Through their own academy - 2.5% rebate per player on their wage bill which the RFL put back into the specific clubs Academy
Encourages home grown talent and investment into English players

Just an Idea

But they need summat to spark their interest before going down to an amateur club.