No idea, when or what any of the criteria is I think the common belief is there should be more emphasis on the Hall of Fame with an Immortal added every 5 years or similar, maybe a couple at a time to catch up in the early years one past player and one reasonably present player.
There seems to be a few worthy candidates:
Provan
Coote
McCarthy
Meninga
Langer
Fitler
Lockyer
I'd be going back and covering the gaps so would do Provan, while he's still with us, and one of Meninga or Lockyer
Cheers
Ross