Support for the Classic Editor
Back in late 2018, it was said that the Classic Editor would be supported until the end of 2021. It has now been announced that support will be extended until at least the end of 2022.
In my personal opinion, the current state of development on the Gutenberg project would make it difficult to meet this revised target. And so, the end of 2023 seems the earliest time for ending support for the Classic Editor to my untutored eye. Of course, it is debatable if even that date will be met. The only thing that you can be sure of is that Automattic will continue to apply pressure on WordPress.com users to switch to the Block Editor.
What is Next?
The basic mantra for phase 2 of the Gutenberg project seemed to be that everything will become a block. While this idea tripped off the tongue very easily, its implementation has been proving far from straightforward, for example in relation to widgets and menus (now called navigation blocks). The first use of blocks in widget areas has eventually appeared in WordPress 5.8.
WordPress 5.9 is due out in early December, 2021. Expect to see further refinements of widget blocks, and possibly the first appearance of navigation blocks?
Full Site Editing is the name that is actually given to the extension of blocks to all parts of WordPress. Work has been going on in this area for quite some time. Perhaps, the big announcement will arrive with WordPress 6.0 or 6.1, somewhere around mid-2022?