From my interpretation of Yoshi wordings, new jobs are still possible with existing classes that do not require expansion. SE must be playing around with the concept of Arcanist having both as Summoner and Scholar and decided that other classes can do the same too. Here's where its a little bit tricky as SE is not usually giving out free new jobs like thief to players that have already level up most or all classes thus the likelihood to increase lv cap to 60 together with the new jobs to get used to them.

As to the location of where to level up above 50, instead of having each new areas for all 3 cities (Limsa, Gridania and Uldah) that will be too large for patches, SE might simply be using one common new area which could be Ishigard. It is situated on a neutral ground Coerthas and is possible as simply a patch thing (2.4 maybe just after Crystal Tower patch). Or possibly giving experience points on new harder dungeons so as not to clogged out all players in one location.