Well, in truth there are two things to affect the outcome
1) Corporate Enthusiasm
2) Developer Enthusiasm

As we see, #1 is an absolute requisite for getting the game done. #2 is a requisite for getting the game done well, for if #1 is large enough a game will be made regardless. #1 simply comes down to one thing, money. The question is weather the Ivalice brand becomes popular enough to boost sales of its own accord, independent of the Final Fantasy or S-E label on the box. This will likely depend on how well the Ivalice Alliance is received. However, it is important to note that this is not necessarily tied to the success or popularity of the individual games, from a corporate standpoint if people do not identify strongly with the Ivalice 'brand' there is no incentive to develop Ivalice titles over any other lore created world. This brings us to #2.

If the developers wish to continue working of the Ivalice brand. Since I know extremely little of the people who design and produce these games I can't say if they a) work on whatever game ideas they like, b) work on whatever ideas they think people would like, or c) work on whatever the marketing people think would make the most money. (Naturally everyone was 'very excited to work on the project' when they do an interview after, so that isn't really a good indication). Anyone who actually knows the corporate/creative structure of SE please educate me.

Of the three reasons for developers to develop the games, c) is essentially what I mentioned in the beginning about corporate enthusiasm. That means we just have to consider if developers develop games to please fans, or develop games to please themselves. In my short but cynical life, I've personally experienced that most creative people fall into a), working on whatever interests them. (Sorry if I defame anyone’s heroes working over there, I don't know them all that well, just generalities here.)

With this said using my reasoning it basically comes down to how much the developers like Ivalice. And since it seems they do very much, as indicated with the Ivalice Alliance, I would say we will most likely be seeing Ivalice for quite some time to come.

Sorry if this post wasn't as abstract or lore focused as you intended, I just kind of spilled out my though process on the keyboard in all its unorganized glory.