>>> I would like to have all at-spi functionality available in Emacs.

This purports to give some.
http://delysid.org/atspi.el

The developer, Mario Lang, sent me the following explanation.

atspi2.el is a client library for AT-SPI2 written in Emacs-Lisp.  
It is meant to write a screen reader, or similar,
in Emacs Lisp.  However, it does not do any toolkit bridge tasks, so
what you are looking for is not implemented/handled in atspi2.el.

>> It would be good, yes. Patches welcome,

>For at-spi2, there seems to exist a D-Bus spec. I'm not familar with
>at-spi, so I don't know whether it is sufficient for Emacs to implement at-spi via D-Bus.

>In case of yes, I could help with such an implementation. Sounds interesting.
>
>> Stefan
>
>Best regards, Michael.