In reply to Matt Mullenweg.

I still think it's unnecessary. I'd leave non-FSE theme users with the traditional widgets system. I could be wrong (and often am), but I would think the users most interested in using block-widgets are going to be those who will also adopt FSE quickly. I'm sure there's a sub-group in there that will want block-widgets but not move on to FSE for a few years. I know it is probably more in line with WP's iterative approach to go this route, helping users along the path to eventual FSE. This will also depend on the theming community. We're putting a lot of burden on theme authors by asking them to start adopting FSE while adding in support for new features for their older, classic themes. Of course, they can opt out, which is what many may do. It will be interesting for me to watch either way. :)

The biggest thing that seems to frustrate a lot of theme developers is the lack of a roadmap that lays out some of these more technical changes. I don't think they are asking for a timeline. They just want a general outline of major feature changes. Obviously, from that one discussion, one of the leading developers from the Themes Team seemed to be caught off guard with the plan and has several unanswered questions.

The widgets system provides a good example of the need for at least a rough outline. If both block-widgets and FSE land in WP 5.7, some theme authors will want to just skip over widgets and start building FSE themes. Others may decide to continue building classic-type themes with block editor and widget support. An outline helps them plan ahead and make informed decisions.