Final answer:
The marketing plan for a sustainable clothing brand should focus on promoting sustainability and ethical practices in the fashion industry.
Step-by-step explanation:
A growing trend being explored in developing a marketing plan for a sustainable clothing brand is the focus on sustainability and ethical practices in the fashion industry. Consumers are increasingly demanding better clothing production practices and responsibility from retailers. The marketing plan would therefore aim to promote the brand's commitment to sustainability, such as using sustainable materials and adopting fair labor practices.