1: Rebuild in Vanilla HTML/JS — NO
Rewrite everything in plain HTML and JavaScript to align with the template architecture, mimicking the other templates. This would mean recreating every interactive component without the benefit of Carbon's tested component library.
Pro: The admin user would have full customizability without requiring knowledge of any component libraries.
Con: There was a high risk of visual regression, interaction bugs, and accessibility failures in a feature being shipped 300K+ users.
2: Carbon Design System Web Components — YES
Carbon Design System offers its components not just as React modules, but as framework-agnostic web components, usable in HTML.
Pro: The web components includes built-in accessibility compliance and preserves design consistency across IBM products.
Con: The admin user would require some understanding of Carbon Web components to customize the templates.
I chose the second option. The Carbon Web Component system was fairly intuitive to understand, and there was comprehensive documentation online. This option also prevented the most egregious UX regressions and allowed a quicker delivery timeline.
Ultimately, this solution provided the best balance between optimal user experience, customizability needs, and client-requested delivery timeline.