What do you think we'll have instead of custom CSS?
* Flexbox being widely supported (a lot of css is just positioning/ordering content)
* Standard style libraries doing most needed appearance stuff in HTML.
* Most brochure sites being sublimated into Facebook for Business/Squarespace/Shopify/Facebook Messenger or some other chat interface. A "nice-looking" website beyond available templates will be worth less and less.
* SaaS continuing to grow and offer hosted solutions for specialized websites/web applications. Already seeing this a lot with restaurants.
* Available React components continuing to grow - you will be able to develop a heavy front-end application using 90% existing modules. React will be bigger than jQuery because of this and because minor use of jQuery for style reasons will fade along with heavily customized CSS.
Web sites get replaced with point and click page creators, in or outside of a platform walled garden.
Web apps have React-based front ends that don't need a lot of custom skinning.