Citing this comic because somewhat relevant:
The Order Grand Alliance is a very mixed bag. "Civilized" or "Good" would not be attributes I'd like to tie to them. How are the DoK more or less civilized than the Gloomspite Gitz, for example?
I would also argue that the Sylvaneth are only in GA:Order because they won't fit into the other ones, and for historical reasons.
I still think that Seraphon belong there. I would even say that they belong there more than most other factions do.
They are paragons of Order, fighting Chaos is basically their only goal.
I also think that a Grand Alliance made up of one faction doesn't make much sense.
About Blood Bowl releases meaning something or not: I still think that we have to make the distinction between Lizardmen and Seraphon. There have been Lizardmen (and other dead faction) releases before, and they didn't mean anything to AoS.
The boxed games that I would call significant to possible AoS developments would be Warcry, Warhammer:Underworlds and Warhammer Quest, because they are directly tied to the lore of AoS, while Blood Bowl isn't.
There was a Blood Bowl wood Aelves team lately IIRC, and those are gone in AoS.
There could be a "Humans of Arabia" Blood Bowl team because it fits the Blood Bowl world, but that would mean nothing to AoS. Hell, the whole old world is gone in AoS but still exists in Blood Bowl.