Follows #44720. Now that layout support is stable, focus is shifting to UI improvements for a more intuitive experience and adding new features, especially for flex and grid types.

UI improvements

• Expanding and simplifying layout #42385
• Drag blocks into other blocks to create patterns and layouts #13202
• Improve consistency of alignment tool placement #49272
• Unify layout-related controls under the same panel #47902
• Streamline the width control on flex layouts #46128
• LayoutPanel: Switch to using the ToolsPanel #44560
• Stack (Group block) variation: Explore hiding the wrap to multiple lines control #43218

New features

• Tracking: Layout Design Tools Consistency #43248 (tracks container blocks that don't yet support layout but could do so)
• Grid Layout Improvements #57478
• Extending AlignmentToolbar Options #27629 (perhaps not so much extending the current toolbar, but providing extra functionality as part of layout support)
• Grid System for Gutenberg #16271
• Grid block: add "auto-fit" option #57186
• Row / Group block child offers dimension width "fixed" which in reality is "proportional" (flex-basis) #53766 (there should be a way to actually set a fixed width on flex children)
• Gallery Block: Use CSS grid instead of flexbox to style the Gallery block #42240 (this could leverage the grid layout type)
• Can not add different content widths for different blocks in theme.json, display bug with alignment control #37124 (allow setting content and wide widths per-block in global styles)

Bugs and code quality improvements

• wp_render_layout_support_flag renders classes on wrong element #57242
• Clean up block gap logic in lib/block-supports/layout.php #52099
• Layout panel options cannot be edited across multiple blocks without data loss #41260
• External stylesheets can't override inline core styles #40159

This is not an exhaustive list but means to track the highest priority features. I'll be following up with some triage to the layout label and may add a list of bugs in the next few days. Feel free to add and edit as needed!