If all coins marketcap was 12 billion at the end of 2013 and 2nd. generation coins can fulfill their goals of spreading much more in to real world from coin-idealist-circuits, there should be 100 times more users and a lot more places and purposes to use it and most of the people would actually use 'em. In that case we can guess that all coins cap could realistically be 1200 billion.

My intuition tells me that there will be 2 major crypto's (just like Visa & Mastercard), which are NXT + some other (hopefully NEM) and they share most of that cap (500 billion each ?) and several middle sized coins will share allmost all the rest of it (190 billion ?) and numerous small coins are left with the crumbs.