Modern BitTorrent can function entirely via DHT and peer exchange. Trackers are supplementary and an optimization. Most torrents you find specify several trackers, and it's fine if some are down. I have a hard time imagining improvements on the current architecture, even under a better copyright regime, which is why BitTorrent has largely stood the test of time.

But it still needs some sort of index to search for stuff, and torrents cannot change. It's a jungle of ever-changing forums and search engines. This makes it harder to pin down by authorities, but significantly reduces casual usability.

There are some tools to index the DHT, although it's limited. But that's more of a result of the regulatory environment and that it's hard to have decentralized search that works well.

There is a spec for updatable torrents, I believe it embeds a pubkey and the creator can announce an update by broadcasting a signed message. But it's not widely used.

It has, with services such as Apples Air Drop and sharedrop.io which are p2p, the ultimate decentralization.

Requiring physical proximity is a big no-no.

BitTorrent got past the need for trackers relatively quickly and hasn't needed them for quite a while now