Mark pegs himself as altruistic and wants to 'change the world', he's also a proponent of guaranteed basic income... I'd like to see blockchain used as a sort of gbi dole system, but it'd need to use reputation / social network effects in order to block 'sybil attacks', ie the bigger your score the more people have 'vouched' you're a real person not a bot or spammer, the more you get out of the daily dole. They also have marketplaces/ads/etc that they could make required to use fbcoin, in order to prop up the currencies prices...

Just speculation obviously, lots of others are trying to figure out a way to do this, but the imposter thing is very real and hard to stop obviously in crypto.