How many more times sigh. The plural of Lego, is Lego. It's like Snow.
From the horses mouth.
My original comment was perhaps ambiguous. You don't say "a Lego". Just like you don't say "a snow".
"Some Lego" "A Lego set" "A Lego brick"
Say after me...
The point of that quote is to (show an attempt to) protect trademark. Like how Google asks people not to use Google as a verb, Lego is asking people not to use Lego as a noun. It's not establishing pluralization rules.
Anyway, I say legos and always have.