The traditional GDP would shrink in the long-term, but the idea (drawing from Charles Eisenstein, Paul Mason, etc) is that gift economies and communities would grow to replace the goods & services we currently rely upon traditionally economic transactions for.
And you're right that policies trying to democratize abundance (unconditional affordances like UBI, healthcare, etc) would restructure the labor force. But David Graeber's 'Bullshit Jobs' is a strong case that the labor force needs restructuring anyway.
And it grows increasingly difficult to earnestly frame these abundance arguments as fanciful, wishful thinking, when some of the most reputable economists who've ever lived argued the same. Thinking of John Maynard Keynes, JK Galbraith, and so on. There's a serious economic discourse, and potentiality, around the idea of lessening the amount of necessary labor to negligible amounts in order to secure access to all one needs, leaving production and 'participation in the workforce' to be an increasingly voluntary decision, taken on because one wants to make something, rather than one needing the paycheck to continue living their lives.
What do you think? The idea of abundance doesn't seem like a hippie discourse anymore, especially in light of folks like Mcafee's work. Why do these ideas continue striking folks as wishful thinking?