Utopian fantasy tends to follow a predictable arc as much in ideology as in technology. The cognitive consequences will be constitutively dissociative and alienating but then, all technology simultaneously empowers and inhibits.
A recent study regarding the shrinking of brains some 3,000 years ago aligns with a general thesis that offboarding cognitive processing power to distributed systems is a symptom (not cause) of accelerating social and cultural complexity in and as collective intelligence.
The (true) cost is likely that subjective identity will be far more prone to pathological disengagement from precisely those newly-minted normative, technologically-mediated subjectivities and experiences. Technology serially does precisely this: inadvertently generates the problems for which it becomes the only plausible (and yet mischievously incomplete) solution; conflict and accelerating technical (as geopolitical) competition being a case in point.
This is all a view into an autonomously self-propagating tesseract of information and energy-processing system that inhabits us at least as much as we inhabit it and for which Meta can only ever be a superficial, transient waypoint on a much longer and more interesting human odyssey.