Just because something is written down, doesn't mean that it is the truth, makes sense, or is relevant. It doesn't mean it's not either.
There's a lot of context needed for that one quote, and there's a lot missing even then.
The problem at hand is what to do about 'guys'. So some facts:
- 'guy'is entirely male gendered. The sentence
?That guy is pregnant
sounds wrong because males do not get pregnant.
'guys' is questionably gendered. It's supposed to mean 'that familiar group of people'. It was losing its gender for a while, being very acceptable for even all female uses, but as the author give many examples, people are starting to shy away from it.
'you' is both the plural and singular second person plural, but has for a long time been more associated with singular, which makes room for a new plural to disambiguate.
Any possible replacement should fit (not necessarily at the same time) the following examples:
Will you please move to the back of the room?
Hey you, go to the back of the room.
To answer your question directly then:
"English lacks a standard gender-neutral second-person plural pronoun." is false because it has 'you', but no one uses 'you' to -address- a group anyway.
So the article is accurate in noting that 'you guys' feels gendered enough to avoid, "y'all" sounds (in most formal and informal American situations) too 'regional' (I doubt it would fly at all outside the US). IN a locative use (addressing a group) many suggestions have been made, but one can use in a natural manner:
- You all
To understand some of that article, make sure to consult these ELU questions: Is 'guy' gender neutral, What is a feminine version of 'guys'?, and especially Did English ever have a formal version of 'you'?