I can only hope that most of the book gets global (evergreen) approval.
I can predict you'll get your wish, if by 'most of the book', you mean the two-thirds of the book that is basically setting material. Other than questions surrounding the Arcane domain, there's not much preventing people who have this book from choosing a deity from it rather than the PH, while allowing players who only have the PH to choose from that list instead. There's even some interesting consideration of why an otherwise 'heroic' character might choose to worship Asmodeus or Cyric, for instance, that might inspire some cool RP builds.
As for the one-third of the book that contains the race/class/background info, it's hard to say. It wouldn't surprise me if a few things were disallowed but later certed (both to allow the admins to keep an eye on particular mechanics without overwhelming the campaign as well as to allow for some 'reward' options for people who volunteer and/or attend cons). I can honestly see arguments in favor of 'only legal for season 4 and beyond' as well as 'legal for all AL seasons'.
Take the svirfneblin, for example. As of this moment, the deep gnome is legal in AL as a Season 2 (Elemental Evil) character option. From a mechanical standpoint, that's not terribly restrictive, as the only Season 1 and Season 3 exclusive options appear to be background options (though given that Season 3 is the 'Underdark' season with appropriate backgrounds, some RPers might be inclined to disagree with me). If SCAG is approved as a 'Season 4+' resource, then deep gnomes have to keep track of whether they were created under EE or SCAG rules, not because the race is different (as far as I can tell the racial benefits are identical for the two versions), but because the different seasons unlock different character options -- a Season 4 deep gnome can't take Season 2 spells, for instance, and likewise a Season 2 deep gnome can't take a Season 4 sub-class. That might seem confusing, but consider the alternative -- if SCAG rules items are declared legal for all seasons, then a Season 2 deep gnome can take SCAG character options, but that doesn't mean a SCAG deep gnome created in Season 4 can take Elemental Evil character options. (You choose your storyline season, and then determine your legal rules sources from that, so just because SCAG might be a legal rules source for any storyline season, that doesn't mean that a character created in a season where SCAG can be used can use other rules sources that aren't available to that storyline season.) That, arguably, is even more confusing.
I don't envy the admins the task they've put before themselves here, and it doesn't surprise me that they're taking their time to get the announcement right before making it.
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Pauper