The new IDE at Repl.it is designed with a small core, easy customizability, and server-side rendering capabilities. The old workspace layout was rigid and lacked configurability, leading to complex configuration logic and maintenance issues. The new design uses a lightweight core that functions as a window manager and middleman for events, allowing components to be bundled into plugins that can expose render targets or internal state management. Plugins are easily customizable and can register their own middleware, making it possible to swap out one plugin with another without affecting the overall system. The layout is also handled by Redux, allowing for easy changes at runtime. Server-side rendering is achieved using Next.js, which makes bootstrapping the initial state from the server a breeze. The new design aims to simplify and correct the core framework, with plans to open-source it in the future and allow anyone to write plugins for it.