It seems as if the cryptarch will progress on a level with gameplay. I figure in the main game, you'll get at least to level 4 or 5 just doing story missions. I don't think rewards scale with level, however it would be nice to see higher ranks of cryptarch giving better rewards - maybe even a max rank? That way, those who are truly dedicated, be it time or kill wise, will be rewarded in tandem with their total game experience.