You also can't be the only seeder on a torrent for the same reason.
The main issue with I have with how the current i2p implementation works is that it essentially creates a walled garden in the torrent network, as i2p users can't seed out to non-i2p users, they can only leech from them. I feel like that would needlessly split the network, which relies on having as many people as possible seeding. Frankly I don't know if its even possible to work around that, but I'll need to see how it plays out. Also, there needs to be at least one person with a port forwarded on any given torrent. utp only peers cannot seed independently, from my understanding.
If this had some sort of option to bind it to a network interface I'd be able to use it with my vpn. This does seem promising though.