I think something to remember is the Argent Crusade is not very big compared to the two main factions. Plaguelands may be mostly recovered but it also needs to hold those lands afterwards as well. I think a player-operated Argent Vanguard might be interesting, maybe, for dealing with the Sha, but where we are now in the lore the Sha aren't a big deal yet I think. Hm.
Taste the sacred steel of FALCHION!