[DiapDealer]

The other point to keep in mind is that accessibility support in mainstream reading apps has almost nothing to do with whether or not EPUB creators should strive to make their EPUBs as accessible as possible. The fact that outside entities in the distribution chain might thwart your efforts to do so is neither here nor there. That's on them.

Accessible EPUBs are a worthy cause whether or not your favorite reading app or rendering engine fully supports all accessibility features. They're not made any worthier by wider support.

As to the original question (which is entirely moot, by the way): there doesn't need to be enough programs on enough platforms to "handle it." An accessibility feature being ignored by a reading app is not straining anything.