They should mainly be worried about their reliability and trustworthiness. They should not worry about article length, as long as it's from exhaustiveness and important content is still accessible.
Serving perfectly digestible bits of information optimized for being easy to read must not be the primary goal of an encyclopedia.
By the way, "AI summaries" routinely contain misrepresentations, misleading sentences or just plain wrong information.
Wikipedia is (rightly) worried about AI slop.
The reason is that LLMs cannot "create" reliable information about the factual world, and they can also only evaluate information based on what "sounds plausible" (or matches the training priorities).
You can get an AI summary with one of the 100 buttons for this that are built into every consumer-facing product, including common OS GUIs and Web browsers.
