Everyone and their uncle says they are going to buy one... but when rubber hits the road, there will be a lot of people that will remove themselves from the buying pool.
A number of people simply won't be able to afford it. I wanted a GD WRX so much it hurt, but my enthusiasm didn't change the fact that I was still in college and $15k was about the limit of what I could afford at the time. By the time I was ready to buy, in 2006, there were different options on the market and gas had shot up by almost 3x what it was in 2001. Everyone was blown away that I chose a GTI when it came time to spend my money despite being that guy that was crazy about Subarus. I also have a feeling there is a LOT of wishful thinking that this car will start at $32k and top out at $37k. The number of people interested will change drastically if/when this starts at $37k.
A number of people will have life happen to them. They'll get married, have a kid, want to start a business, etc that will leave them wanting the car, but it just isn't a good fit for their life at that time. I followed the FR-S crazy close from the time the concept was shown in 2009 until the release in 2012. Timing was wrong because my wife and I were trying to have our first child. I eventually bought a new 2015 when my daughter turned 2 and could go front facing, but my enthusiasm for the car didn't change that it didn't make sense for me at launch timing.
A number of people will see the instrumented tests and realize the performance numbers are very similar to a WRX, Civic Type R, chipped GTI, STI, etc. While there are a lot of cool things that Toyota did to this car, there are a lot of buyers out there that simply can't handle not having the bragging rights of the fastest car in a segment. This will probably do well in the segment performance wise, but it won't be a world beater. There is going to be more speed available for less money.
A number of people will drop out because they are contrarians. If everyone else likes it, it must be bad. Or it's too mainstream in the enthusiast circles. Or the 3 cylinder isn't mainstream enough! People come up with all sorts of reasons to not like a car and, I assure you, they will be vocal about it! Peer pressure is a thing.
There's no reason to stress about it now. We don't have pricing, we don't know what availability is going to be like in the fall, and we've been subjecting ourselves to an echo chamber of tons of people swearing they are going to buy it without even having sat in the standard Corolla HB. On paper, it looks great, but we have a lot of claims of people buying without actually having any driver impressions or pricing.