In "Parable of the Sower," Octavia Butler (1993) wrote: "Any Change may bear seeds of benefit. Seek them out. Any Change may bear seeds of harm. Beware" (p. 116). In this paper, we apply this command to a speculative examination of the consequences of text-based generative AI (GAI) for adolescent writers, framing this examination within a socially situated "Writers-in-Community" model of writing (Graham, 2018), which considers writing as both an act of individual cognition and as situated within concentric circles representing nested social, material, and cultural contexts for writing. Through the lens of this model, we discuss representations of language-related technologies in works by several well-known authors of 20th-century speculative fiction and contrast these speculative scenarios with examples from our recent research into student writers' use of ChatGPT and other GAI tools. Finally, we discuss (a) the limitations of these tools as lacking the ability to set goals and use these goals to compose a written work, which is a key component of an effective writing process and (b) what would be required to supporting students to write agentively in collaboration with these tools, despite these limitations. This discussion focuses on three principles: (1) centering human writers in collaborations with GAI; (2) setting writer goals to address historical, political, institutional, and social influences; and (3) critical agency in literacy with GAI.