As per Whonix - Advice on Accessibility for a Debian Derivative, the following packages should be installed by default.
gnome-orca espeakup brltty brltty-speechd brltty-x11 console-braille florence dasher kdeaccessibility kvkbd kmousetool kmag kmouth jovie xbrlapi festival qt-at-spi
Makes the images ~ 73 MB bigger. (Installed using apt-get --no-install-recommends.)
Installing these by default probably makes only sense in Non-Qubes-Whonix, as in a Qubes environment, these would have to be installed by default in dom0, I think.
(These should be installed by default, and manual installation is not so useful, because the people requiring these tools in the first place, are not capable to install them by themselves without help of a third person.)
[Especially for users requiring to use Tor Bridges, and a Non-Qubes-Whonix-Gateway, this poses a difficult to overcome obstacle. Recently got a mail by such a user.]