I have to agree with mxxxxxx, a central core or group of currencies that compose the core however, might be best.
What advantages do you see in a centralised approach?
The Blocknet is open and democratic (non-centered) because it needs to be an open and indefinitely extensible framework.
After all, why go through a core currency network when all of them will work just fine?
I though of that after a while in the future(having a core group of currencies), in the blocknet would become diluted? If every currency was equal, then ones without features could be added and not provide any extra service that coins with features(XC) would provide. Also having a core woul act as an incentive o obtain those currencies.
Maybe it could go by a decentralized ranking system, where currencies that contribute the most are placed in a higher pecking order in the blocknet, solving the issue of incentive to buy those currencies and dilution?