The block-based widget editor is a new feature coming to WordPress 5.8. I took a look at the release candidate and found a number of issues. What I realized is that this is a bigger change than many people realize.
The video has a full walk-through and discussion.
Points for Discussion and Conclusion from the Video
Up to now, what I’ve heard about this new feature, the ability to use blocks in widget areas, is just how much more flexible that will be for end users and I can see that. The testimonial blocks (that worked) were attractive and this new feature unlocks more design and layout options. However, what I haven’t heard is just how big of a change this really is.
This is opt out. There are three options for doing so: the theme can disable the feature like we saw with Blocksy, there is a filter you can apply, and there is a plugin to disable it. But you have to take some action.
Remember, none of the themes functioned fully on the dedicated widgets page, which means what? That every single theme currently on offer has to be updated to make it work? That’s huge.
As we saw with the Qubely testimonial block, not all blocks show correctly in the sidebar, so there is work for at least some plugin authors. Now, I was using three core blocks which presumably had been tested to work in the widget areas. I also used testimonial blocks, which are a step up in complexity from the simple core blocks. I tested, but did not show, doing crazy things like adding blocks for rows and columns, and as you can imagine, it was unwieldly, if it worked at all. We all know that end users will try to use any block shown. So, there is no way to exclude a block or mark it as unsuitable for widget area use.
That’s my quick look at Block based widgets. Theme and plugin authors, site builders, site administrators, and site owners have time, but action is necessary. It is probably a good idea to check if your theme will be ready or if some action is needed.