Creating this tracking issue to gather together several blocks that have been proposed over the years for inclusion in core that have been sitting in limbo due to technical blockers or worries about their relevance.

As mentioned in another thread, I think we need to become a lot more practical about these:

I think not having these blocks in the core library severely limits the expressiveness that theme builders (and users) can depend upon to build great designs and it can fracture the overall experience, forcing people to go for more fully equipped block libraries instead or desist altogether if they plan to release something broadly. One of the promises of blocks is that we can finally make themes interoperable without dulling down expression. A separate plugin for these blocks won't help much if a person needs to release a theme or a pattern in the directory, cannot rely on the presence of the block, or is excluded because it doesn't use core blocks.

My opinion is that we should add a lot more blocks and revise a stance that I think harms adoption in this day and age.

It has also been the case that several plugins, whose main purpose is not really about offering design tools, have had to resort to building their own block primitives for things like slideshows, accordions, and so on if they needed to offer patterns to its users. This isn't great for the ecosystem and long term leanness of the platform.

We should also consider making further improvements to the block library manager, so that the default set of blocks can be more easily managed programmatically by site owners, in blueprints, in other WP config, and in a more permanent place in the interface like a "blocks" screen under plugins.

• Icons Block — Add an Icons block #16484
• Playlist Block — Add Block: Playlist #805
• Slider / Carousel Block — New Block: Slider Container (CSS based) #43369
• Stretchy Text — [New Block] Stretchy Text #71017
• Tabs Block — New Block: Tabs #34079
• Accordion Block New block: Accordion block #21584
• Mega Menus — Navigation block: Make nested menus fully customizable (Megamenus) #23745
• MathML Block — Add MathML Block #47198
• Marquee Block — Scrolling Marquee Block #41730
• Time to Read Block — Stabilize Time to Read block #53776
• Breadcrumbs Block — New Breadcrumbs Block #21943
• Dialog Block New Block: Dialog Popup #61297

(This list doesn't imply these blocks are ready, we should continue the conversation on each so that we produce the best versions.)