I think the question isn't really how big an increase will the game get because it's obvious there is almost no interest in this game still (if this game really was going to x20 it's entire population there would be a ton of interest on all XIV forums), but how long will SE run it at a loss before going F2P. They won't shut this down after all the money spent but there is no way they can continue to run it at a loss long term. Especially when the players will demand more and more content and money spent on it.
You repeatedly say there is no interest in FFXIV.
1) There's no data for your claim.
2) We are still in the time BEFORE the 2.0 marketing campaign.
I think you are perceiving no interest because there's no board activity. There's no board activity because there's no news to talk about for new potential players aside from "should I return?"
I'm not saying there's a big interest waiting, but I can guarantee there will be, at least for the first month or so. You can always count on MMO jumpers when any new MMO is released, not counting the people who would get a free first month for already owning a copy.
The real question is, what kind of numbers can we expect in month 2, 3, 4 and beyond?