Well, there's not really anything we can do beyond the forum, so I'm really not sure why its a ten page discussion at this point.
As for dub-only watchers… well, isn't the dub still only on like water 7? Yeah, if they search out OP at all, since they're like 7 years behind, they're going to be spoiled if they see any screencaps or merchandise or pretty much anything. Hell, Strong World shows Franky and Brook in the crew and Luffy's gears.
But if they're such casual fans that at this point they're still only getting the funi dub dvd releases? Or the Toonami airings? Not even the simulcast? They're probably not the types actively seeking, talking about, or stumbling across that kind of stuff anyway, not the sort to be subscribed to multiple threads and news sites that would actively talk about this anyway. (Though the fact they're on like the 300th episode and 40th dvd set means they probably should look into the expanded fandom.)
At some point its okay to talk about the fact the Darth Vader is Luke's father and that Rosebud was a sled.
You can't try to force the entire world to hold back on info on the chance that someone a decade behind the material, who happens to be looking up information on that material, will be spoiled.