Here is why though:
1. ES works. Best selling sedan worldwide. It gets more of the same, just more and better and newer. It works. It competes much better against what has become a fleet sedan market essentially. It is quiet, not offensive, luxurious, fast enough and frugal and has a lot of space in the back. In fact, this is what every LS owner now says they want - they dont want unique looks, sporty handling or fast response... they just want big luxury barge that sails through roads, dont they? Seems like perfect vehicle for typical Lexus driver. Plus with TNGA, it will actually handle fine unlike before. I am sure interior will exceed previous version by far.
2. 3GS and 4GS did not work. It ggot 2 generations that were different and still did not work. I had 2007 GS and I liked the car. 2012 was better in every way, it had a lot of space in the back, it handled best in class... and still did not work for Lexus. At the time, I liked 2012 model a lot. F Sport especially. Now it looks very conservative vehicle. Updates actually made it look worse.
They cant really win, can they? If they release 5GS as 4 door coupe, then people will complain about lack of space in the back, like they do with LS. Some wont like unique looks. Some will say it is bumpy and they dont want to hear sound of the engine. How can they win ever?
It wont be too wrong for them to cut their losses. But they wont because their RWD cars make sense since they sell 3 of them + new SUV. But yeah, I bet many people will complain that new GS is too sporty and lacks headroom with pano roof.
I don't disagree with what you are saying. This is a business at the end of the day, and ES is the better case -- period. What will be immensely problematic for Lexus is going to be the global media reaction to this car. You can say I'm reading tea leaves and no, we haven't seen the final car yet and there is still much unknown about it, but...
If they introduce an ES that looks like this and remove the GS completely, this new ES will be torn to shreds by the major media in the US, let alone Europe. Lexus will state the competitive set is the A6 and E Class, and it will probably not fare very well against either. Let alone the 5 Series and whatever Genesis model it competes against... G80? E class is more elegant as a scaled down S class, and the A6 - while also bland - looks more aggressive and has better detailing and execution. US media will probably compare it most directly to the Buick LaCross. There will certainly be a FWD model of ES, but who knows what type of AWD will be offered - we can speculate all day. I am not expecting a transverse mounted engine considering the long front overhang we've seen in spy pictures, and that's sad because it would likely help how the car drives by eliminating torque steer.
All of the media reviews will mourn the loss of the GS and say that the ES is not as good of a car as Mercedes and Audi. Too boring, too bland, FWD, doesn't drive well, etc. Then it will be more expensive than the Buick, and they'll probably complain about that too.
Now, we can also say that media doesn't matter. Does it? I think yes, and I think Lexus underestimates the value of positive PR quite heavily. You will bring up all of the positive press for the Honda Accord and how that hasn't translated into sales. There are lots of other important factors like leasing and financing options, and a polarizing design.
My point is this: This ES will surely continue to be successful, and it will continue to sell to people who have bought ESs in the past. However, that is a bit if a niche market in between RWD entry level sedans and midsize premium sedans like E, A6, 5er, etc. Lexus has been able to cover all of those bases with IS, niche ES, and GS, but when they remove GS... it just doesn't seem that they've done enough to properly elevate the ES if it looks like this. This car will not sell to the GS buyer, and quite frankly, I am not sure it will really compete with E Class. FWD A6 variants? Maybe.