If at all—is there a way to know when the player options in SCAG will be available in AL? According to the latest AL Guide I found, only PHB and few other minor resources are allowed.
The Sword Coast Adventurer's Guide is, in fact, already allowed material for Adventurer's League. It does not appear in the current AL Guide because it was published after the current AL Guide. However, AL put out an announcement about it. You should read the link, but:
Everyone, regardless of story origin (season) has the possibility of using the options presented in the Sword Coast Adventurer’s Guide. Add the allowed portions of the Sword Coast Adventurer’s Guide to the list of allowed rules for every story origin (see below).
Also, note that:
The D&D Adventurers League Player’s Guide will be updated with this information next season.
In other words, they're not going to bother with a revised Player's Guide this season, but from next season onwards the Player's Guide will include SCAG as an allowed option.