I'm chiming in late here, but our icons are in the PUA, and therefore have nothing to actually "read". aria-hidden is not necessary in this scenario; it is only needed when you are using unicode characters that can be read by a screen reader as something (eg. the caret glyph is read as "n-ary logical and"), but don't want it to because it is ornamental.
I have a
test version of something in Flow now, which allows us to just put the text inside the icon's element as plain text. This gets read fully by screen readers. The alternative to this would be to use <abbr> as the icon element, which gets its "title" attribute read by almost every reader.