Well, isn't that sort of mentioned in the article?
If fediverse development slows down e.g. because adoption of inofficial Facebook extensions takes time it will harm the whole platform. Not by directly taking away users but by blocking progress.
I don't think the Fediverse is small enough for this to be a serious concern. Especially once multiple companies (Tumblr?) are invested in the fediverse I don't see this happening anymore.