This paper's five-aspect design space (task, user, technology, interaction, ecosystem) and its systematic review methodology have served multiple roles across subsequent research: as a structuring framework adopted by researchers building design spaces in adjacent domains such as AI-assisted music creation and dialogue augmentation; as a practical guide for designing new writing tools, with its interaction dimensions, writing stages, and feedback types informing systems for reflective writing support, educational argumentation assistants, professional co-writing interfaces, and mobile LLM text interaction; as the source of the tool–agent–hybrid interface metaphor taxonomy that subsequent work has extended and empirically tested and applied to study user perceptions; as a reference for user-centered concerns like ownership, agency, and trust that motivate designs prioritizing psychological ownership and writer control in co-creative settings; as a framework for understanding the sociotechnical ecosystem surrounding writing tools, cited in work on deployment contexts for educational writing AI and regulation-aware system design; and as a landscape survey that contextualizes the rapid growth of LLM-based writing assistance for researchers studying scientific writing, creative storytelling, and human-AI collaboration more broadly.