> .. I think the incentives should instead encourage variety and availability like a distributed, highly-available, P2P archive.

Which is exactly what it is like for many trackers these days. They have an "economy" where some type of bonus point system allows you to buy upload credits. You often acquire this by either simply seeding over time, or by uploading special torrents with rewards, eg double upload credits, etc.

Some trackers even double down on this concept and basically only care about long term seeding. Ratio doesn't matter as much if you're seeding 24/7.