We are now seeing the following message at the top of the Lightning Web Components Playground:
Playground will be retired on February 1, 2021. All saved projects will be permanently deleted at that time. Instead, try a third-party solution such as webcomponents.dev to edit and preview your components in a browser. We'll be publishing a blog soon with all the details.
Obviously there's an important blog entry pending. The blog will probably get most of us up and running with the new recommended way of doing browser-based LWC futzing.
In the mean time, are there any trailblazing StackExchange contributors willing to initiate us (erstwhile) Playground fans on how to get started with WebComponents.dev + LWC? Or similar tools we might consider using?