Web accessibility rests on static standards and developer compliance. That model frays in platforms where content is user-generated: photos arrive blurry or off-frame, descriptions skip size and condition, and page structure shifts from listing to listing. Drawing on six studies conducted between 2022 and 2025 with blind, low-vision, and older adult users of customer-to-customer (C2C) marketplaces, I argue that generative UI can produce adapted interfaces at the point of use, addressing barriers that static design cannot anticipate. Three interventions from this program -- HTML regeneration for screen readers, conversational guidance for older sellers, and audio-guided photo framing for blind sellers -- demonstrate how runtime generation can bridge gaps that standards leave open. I outline what these findings imply for HCI practice: generative UI extends beyond the screen, complements rather than replaces ability-based design, and shifts the designer's role from specifying layouts to specifying policies. This is an expanded arXiv version of a position paper accepted at the CHI 2026 workshop "What does Generative UI mean for HCI Practice?"

翻译：网络无障碍依赖于静态标准和开发者合规性。但在用户生成内容的平台上，这种模式显得脆弱：照片模糊或偏离框架，描述缺少尺码和状态，页面结构因商品而异。基于2022年至2025年间对客户对客户（C2C）市场中的盲人、低视力及老年用户进行的六项研究，我认为生成式用户界面能在使用点生成自适应界面，从而解决静态设计无法预见的障碍。本项目中的三项干预措施——针对屏幕阅读器的HTML重建、面向老年卖家的对话式指导以及面向盲人卖家的音频辅助拍照——展示了运行时生成如何弥合标准遗漏的缝隙。我概述了这些发现对HCI实践的启示：生成式用户界面超越了屏幕范畴，并非取代而是补充基于能力的设计，并将设计者的角色从指定布局转变为指定策略。本文是CHI 2026研讨会"生成式用户界面意味着HCI实践的什么？"已接收立场论文的扩展arXiv版本。