Lighting and colour would be the big one. Might be out of scope for "underpass revitalization" specifically, but addressing the unfavourable signal timing for pedestrians and cyclists at both 9th and 10th Avenues would be a big improvement. As a downtown resident I get frustrated daily with every signal that is set for ridiculously long green-wave/lengthy advanced green turning phases when that capacity is only needed 2 hours a day. The other 22 hours it punishes residents and active modes dis-proportionally by delaying north-south walking and cycling significantly on 5th Street (and others)