Have you heard about ArcGIS Experience Builder? It was first previewed at the 2019 Esri Developer Summit (see more details here: https://www.youtube.com/watch?v=R9o1e5eGX_A). If you love Web AppBuilder, you'll love this next generation product that introduces a whole new way of building web apps. To get more information and receive announcements about the beta, sign up for the mailing list: ArcGIS Experience Builder | A new way of building web apps
P.S. There are no plans to replace or discontinue Web AppBuilder. Both builders will be running and maintained in parallel.