Combining the Trimet datasets/services with the datasets pertaining to curbs, sidewalks, and slope/elevation would allow a user to plan an "accessible" trip.
Walking or otherwise traveling to a station that's technically the closest one may not be the best option if it's a 50ft elevation gain or the travel path has no sidewalks or curb ramps.
The solution is a front-end to the TriMet trip planning services that picks the best routes and walking paths for those that are in a wheelchair, walker, scooter, or would simply prefer not to hike up a hill if it's not necessary.
Evaluating a series of available routes and weighing them based on the user's preferences - elevation, sidewalks, curbs, etc - would be a fairly straightforward task.
This could also be useful for those traveling with children that don't want to walk along the edge of streets with no sidewalks.