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Accessibility with Blossom's Canvas based UI
The W3C has already decided on providing navigable, accessible DOM below the canvas element. (You can read about the decision here: Working Group Decision on ISSUE-74 canvas-accessibility.)
Note: this only applies to the SC.View surface type, which is the only surface that hosts a layer tree of Canvas-based UI elements in Blossom. All other surface types map 1:1 to DOM nodes and thus support Accessibility in the usual manner, without any difficulty.
Blossom's approach is to provide a simple, unstyled and semantically-correct DOM representation of an SC.View's layer tree below SC.View's Canvas element. Assistive Technology can access and navigate this DOM tree, and the results are reflected in the layer tree using the normal Blossom mechanism (e.g. firstResponder). Text is also represented in the DOM, for screen readers.
Preliminary technical feasibility has been done, but a specific API for Blossom has not (yet) been decided. In part, this is pending on the native runtimes with the goal of supporting Accessibility equally well on all platforms, not just web browsers.
Accessibility is a priority, and we anticipate a full implementation in the Blossom 1.2 timeframe (the next stable release after 1.0).