I'm willing to be proven wrong, but I don't think we're getting the PS5 Slim in Q3 or Q4 2023.
The new unified PS5 model was announced by Sony for September this year so that kills any and all arguments you have. How the design will look currently is anyone's guess, but it makes sense it will be smaller in size, probably keeping the "artistic style". Making a new case costs you money first, as you need new press forms . Savings on case material will be in the very low $ range, but we are not even close to halfway through the PS5 cycle. Original press forms (my guess is aluminium) don't last forever so the manufacturer(s) would need new forms anyways from time to time. And the new model has only one size (no disc), so only one set of press forms is needed in the future. It is more than sensible to change the form factor now while there are still dozens of millions of PS5s to make.
The money changer is the reduction of the chip. If it's down to 6nm, it's only about 10-15% less current for the SoC compared to 7nm as it is now, but since P=I^2*R, that means around 40-50 Watts less to get rid off. That could make the case considerably smaller and cooling simpler (=cheaper).
Whether you call the new model "PS5 Slim" or not is not important, my guess is it will certainly be smaller than the current disc version.
This, and there's also the fact that PS is selling a bit less games, and games and services are where the money is made, so if more consumers can't get the console, you're leaving a bunch of money on the table. This makes it more worth it for Sony to push for new advanced chips even if it's a bit more costly. As long as it's not too much more cost, they can justify it because it'll mean even more consoles can be manufactured and sold, so even more games and services can be sold. Plus if you've got (cheaper) competition like the Series S with Game Pass, and a potential recession coming, then all the more reason to get more (cheaper) hardware out asap.
@Zippy6 Yes, but it's a combo of being big enough to have cooling and the manufacturing process.
A PS5 released at launch that is as slim as an inevitable PS5 Slim would be way more expensive if it had the same specs and cooling. If Sony wanted a slimmer PS5 at launch, they would've had to compromise on cooling and specs.
When certain specs and cooling no longer require a larger shell, that's when it becomes more profitable to make the product slimmer.
You have to consider that the launch model should always be overkill because a poor start due to poor hardware design just makes for a bigger headache for the rest of the gen. Going a little overboard at first is worth the little you could've saved.
You also have to consider how much the casuals care about the system temperature and noise vs the cool Slim factor, in which case they don't care as much as most of the more hardcore early adopters. Even some of the more hardcore prefer the smaller form factor regardless if it runs a bit hotter or louder. Due to this, Sony could design the Slim model to run hotter and louder and it wouldn't matter much, as long as it's not too hot or too loud. They would basically have to make sure it's a bit quieter than a PS4, and run cool enough so it lasts a bit into next gen, and it will still sell like hotcakes being much smaller than some may anticipate vs the present PS5.