In recent years, high-entropy alloys (HEAs) have rapidly progressed from being mainly of academic interest to becoming serious candidates for advanced applications, including hydrogen energy systems, fusion reactor walls, additively manufactured turbine components and biomedical implants. However, two significant issues still limit large-scale adoption. The first is the research-to-implementation phase, which refers to turning atomic-scale breakthroughs into reliable, qualified components at the industrial level. The second is the sustainable design-performance deficit, which involves achieving exceptional properties without causing environmental or social burdens. This chapter is grounded in the 2025 literature surveys atomistic-to-component mechanics, additive manufacturing microstructures, hydrogen and metal interactions, radiation tolerance, creep maps, machine learning pipelines and nine-dimensional sustainability metrics. It closes with an actionable 2035 research roadmap that positions HEAs within a circular economy.