Yes, we consider accessibility a must-have feature. On the web, we have a second DOM tree called the SemanticsNode tree, which is generated in parallel to the RenderObject DOM tree. The SemanticsNode tree translates the flags, actions, labels, and other semantic properties into ARIA attributes. We've been testing Windows Narrator, VoiceOver, TalkBack, and ChromeVox screen readers to navigate a Flutter web app.
So why is FlutterPlasma.dev completely unusable with a screen reader even after pressing the "turn on accessibility" button? I understand that the actual demo presentation might not be accessible, but the intro screen should be fully readable, and it's not.
Edit: You may want to add the NVDA open-source screen reader for Windows to your list. And when you test with a screen reader, make sure you use it the way an actual user would when browsing the web, e.g. using NVDA's browse mode with the arrow keys to move through the page.