I appreciate all of the comments; still unsure where to more persistently host the conversation, but for now I posted this still-arbitrary list on Commons. (adding other items mentioned in this thread) SJ

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- File formats: Support high-demand formats – e.g. CSV, CML, + hundreds of other open tickets

- Uploads: Improve bulk, large, and video uploads.
+ Bulk conversion for video uploads (videoconverter / video2commons are broken)

+ Upload Wizard upgrades (timeouts, batch renaming, batch imports)
- Downloads: Fix multi-download (Imker is broken)
+ Make public dumps (stale since 2013)

- Video playback: Debug + roll out the videojs player
- Search: Bring CQS back up. Implement a noauth option for tools

- General: Move to a blazegraph alternative (for wqcs)

+ Images: Update thumbor and librsvg || redesign the image table

- Curation: Simpler content assessment workflow, like en:wp's (QI/VP doesn't scale)