  Compelling writing is tailored to its audience. This is challenging, as
writers may struggle to empathize with readers, get feedback in time, or gain
access to the target group. We propose a concept that generates on-demand
feedback, based on writer-defined AI personas of any target audience. We
explore this concept with a prototype (using GPT-3.5) in two user studies (N=5
and N=11): Writers appreciated the concept and strategically used personas for
getting different perspectives. The feedback was seen as helpful and inspired
revisions of text and personas, although it was often verbose and unspecific.
We discuss the impact of on-demand feedback, the limited representativity of
contemporary AI systems, and further ideas for defining AI personas. This work
contributes to the vision of supporting writers with AI by expanding the
socio-technical perspective in AI tool design: To empower creators, we also
need to keep in mind their relationship to an audience.
