- Apparently Vuze now bundles with an I2P plugin that doesn't require installing I2P manually. Since mid of march this lead to a significant boost in the network size http://stats.i2p/pix/total/leasesets-year.png (http://pix.academ.org/img/2015/04/02/312a4be8ef17065c0cbdb5f91df66d2e.png). Due to DHT support, you can take a popular clearnet torrent magnet link, feed it into I2P's bittorrent client (I2PSnark) and download from Vuze peers.

- Another I2P implementation in C++ is developed https://github.com/PurpleI2P/i2pd (allowing I2P for example to run on weaker routers, where Java is too heavy).

- There are rumors of Popcorn Time switching/supporting I2P.

Maybe these are the killer applications that allow I2P to grow large like tor?