When I first contacted jl777 after hearing about his plans for the superNET, I was incredibly excited not only because I believed it needed to happen but because I was hoping that the solution to the lack of communication between blockchain technologies would be decentralized. What superNET offers is to act as the decentralized network that allows other decentralized blockchain based technologies to communicate.

Imagine that you have a big room full of instances of blockchain technologies (for example crypto-currency wallets (btc, ltc, nxt etc), storage programs like storj, or anything else that people may come up with in the future that makes use of blockchains). As it stands now, all of these technologies would be running independently of eachother (or floating as I've seen you describe it) without any means of knowing about the others, or making use of the other's technology.

The superNET may act as the messenger between these blinded and independent technologies. Right now if you want to use the features of BTCD to perform anonymous transactions, or use the staking coin storage abilities of coins like NXT, the asset trading market of NXT, domain name services of Namecoin, encrypted messaging of Opalcoin, the decentralized cross-chain ledger of  ATOMIC, etc (the list goes on and on and you probably know of even more examples of new technologies than I), then you would need to go and download, install and sync with the blockchains of all of these wallets. superNET will allow you to use all of those features in one place, without acting with central control (as all of those blockchains will remain independent) Another way to think about it would be that you have several major cities (Bitcoin, BTCD, storj) each offering their own attractions (the most secure ledger of Bitcoin, the anonymous transactions of BTCD and the storage of storj) the superNET is the system of highways that will allow people to not stay in just one city, but allow them to venture out making use of all of the attractions and  hopefully it will encourage developers to actually make useful features out of the blockchain technology, now that they are more accessible than ever.

Here's a great article that might help out in understanding as well: http://bitcoinmagazine.com/18167/what-is-the-supernet-jl777s-vision/