A different approach could be kind of a "flattr" model for paying uploaders.
Seeders of anything run a client that replies with their ID and downloaders run a client that asks any connected client for that ID (it either gets ignored or someone replies). Every now and then a list of "I loaded 1 MB from X, 40 MB from Y and 100 MB from Z" is uploaded to service.com.
Service.com then holds funds of downloaders in escrow and pays them proportionally to X, Y and Z. If downloaders don't tell any data, their funds for that time frame get donated or evenly split or split according to some rating (glicko2 sounds really cool) or
. Stats should be as fast as possible available but aggregated over a week or even longer (2 weeks, 1 month...) to have meaningful data for payouts for most participants.
To get more funds, it is of course better to prefer clients that ask for an ID. It can be even 2-sided, so seeders can also see if they really got paid something from A, where they uploaded 1 GB to or if A was just asking for their ID but never submitted a report.
This would again require some trust from seeders, that someone asking for an ID will really pay something and requires 0 trust from leechers (as they anyways can use the swarm as usual - but have a chance to get some much better seeds if they ask for IDs to pay towards). If the updates run in near-realtime, trust can again be increased over time ("I uploaded 1 MB to A and a few seconds later A rightfully told service.com about it - more bandwidth to A!") and even without some fancy traffic shaping stuff it's simple to just seed some popular torrents and potentially gain a few coins too.
This way it doesn't matter if there are fakes or not (they can only pay anyways) and service.com also doesn't need to care about bandwidth offered as it is i the best interest of seeds to offer more bandwidth to users of service.com.
The above would be the other extreme - big torrents with few leechers would be not very popular, unless there are some leechers that really offer a lot for that traffic. Just keeping the torrent alive though (no leechers atm.) is not really attractive, as there's more money to earn by loading + sharing the next file and actually uploading something.
Maybe these 2 extremes (it's already enough holding a file and not even seeding it vs. upload is everything, even just loading 1 part of a popular file + just sharing it can net you a lot) can/should be somehow combined for different user groups or so?