I would say reusable HTML components (think widgets like carousels, maps) which allows users to customize CSS would be a better investment than building themes.

I would say reusable HTML components (think widgets like carousels, maps) which allows users to customize CSS would be a better investment than building themes. disclaimer: I'm building a new CMS called Pragma (https://pragma.build https://pragma.build) which would allow users to compose pages by assembling components.