In fairness, there are at least rumors that snow-jax might be a more or less official source. But then, there are rumors we might be getting it along with The Source later this month, so who knows.
I can kind of see the frustration with spoilers that've been out for a while (people getting too far ahead of themselves and forgetting the moment), but honestly I don't think wanting to know all the cards in a given pack ahead of time is unreasonable. Some folks can't get all the packs, and they should know in advance what they're getting.
Maybe this is experience with Magic, though. They spoil things in drips and drabs, but by about a week or two out -- which is approximately when snow-jax tries to drop spoilers -- everything is up to be seen so that people can know what they want to be testing and jump right into things when the release hits.
Now, they do draft/limited as a major selling point, and that requires a deep knowledge of the whole pool, but still. If we had the whole of the SanSan cycle spoiled before The Valley hits I don't think I'd mind overmuch (though the obvious playtester spoilers are still a serious no-go, I'd say).
That said, do wish there was a way to toggle/warn that on OCTGN. Roomie had a game against Chronos Protocol a couple weeks ago when testing a Leela deck, and it ate him alive because he wasn't expecting to deal with it. It's like playing the Collective (neat, and honestly looking less horribly busted by the day), it's cool to see, but it's not even out SOON.
EDIT: To clarify my above meaning a little more...
I am not opposed to getting SanSan and/or the next deluxe box (or whatever is done enough to not be tested further) spoilers if FFG releases them.
I am opposed to people actively breaking their NDA and making things worse for other playtesters, like the person offering/threatening to do that on Reddit was, because that's just not right.