We actually use plain standard HTML and ARIA attributes for accessibility. If you don't see them, try enabling a screen reader (e.g. TalkBack on Android, VoiceOver on iOS/macOS), then you'll be able to enable accessibility in the app. If you are having problems with a11y, please file a github issue. A11y is very important to us.
https://api.flutter.dev/flutter/material/SelectableText-clas...
I personally expect this trend to continue, as in most desktop native apps text is not selectable either. In fact, in many web apps (those that are really _apps_, not just static web-sites) there's lots on non-selectable text. Case in point, I just checked Gmail's landing screen, and I failed to find a single piece of selectable text.
Does selectable text have a performance penalty? In iOS UILabel is far faster to render than UITextView, but only UITextView is selectable. I wouldn't mind if many of my UILabels were selectable, but I'm forced by performance constraints to not let it happen.
Maybe put forward making SelectableText the default and renamed to Text and Text is renamed to UnselectableText and becomes the non default if there isn't a perf penalty? It would need an automatic migrator for that to happen although.