The capstone is not a study. It is one barrier removed, with evidence. That changes what a good choice looks like. The barrier should be recurring, so that fixing it changes many experiences rather than one. It should be specific: a meeting series, an intake step, a document set, an accommodation process, a hiring stage, not “accessibility in our division.” It should be within the team’s combined authority, which is why the team is cross-functional; if the fix needs communications, information technology and a supervisor, all three should be on the team. And it should be felt by identifiable groups, so that the people affected can be brought into the design and can tell you afterward whether it worked.
The best source of candidates is what disabled colleagues and participants have already said. Barrier reports, accommodation requests in aggregate, steering committee recommendations and the things people mention in passing are a list of real problems with real people attached. A team that picks from that list starts with credibility; a team that picks something it finds interesting starts by explaining itself.
The problem statement comes before any solution. Four sentences: what the barrier is, who meets it, what it costs them, and how often. The affected-user analysis extends the second sentence: which groups, in what numbers where you can estimate them, meeting the barrier in what way, and who among them is affected most, by language, geography, income or other factors. Resist writing the fix. A team that writes “the meeting needs captions” before it has mapped the barrier will solve the first symptom it noticed and miss the rest.