8x1Ghz A72 would be nowhere closer to the 8x3.6Ghz Zen 2 CPU of current gen, and the 8x2Ghz A72 is plain unrealistic for a portable device. Moreover, 4x2Ghz is not slouch and would put the Switch on the top tier CPU mobile performance, being not much slower than the Steam deck and more powerful than almost all non-Apple mobile devices. Also, I do not believe that 4x2Ghz would fare worse against 8x3.6Ghz Zen 2 than the 4x1Ghz A57 CPU did against the 8x1.6Ghz Jaguars.
I would not be surprised if we get 4x1.5Ghz A72 CPUs, and it would be a much more stronger CPU for its time than what the Switch launched with. The difference is that the PS4/XB1 launched with crap CPUs for their time, so 4x1Ghz A57 could still get some ports, while the PS5&XBSX are the most powerful consoles for their time we have ever gotten.
It would certainly be an interesting move to use A72s in a product releasing in or after 2022, haha. I'm guessing that's a mistake?
My understanding is that A78 is similar in performance per Ghz to Zen 2, just as A57 was similar to Jaguar. So that makes the comparison math easier; Switch with TX1 is roughly one third the CPU strength of a PS4, while 4 A78 @ 2Ghz would be a few points over a quarter the CPU strength of PS5. So the gap would be similar, but grow slightly rather than shrink. Obvious caveats with this sort of simple comparison exist, but it's enough to show us an overview.
One thing I've forgotten to mention is that we can expect Nintendo to continue reserving one core for the OS. With four cores that would be a quarter of the CPU, with eight cores it would be one eighth. So the difference in power available to games is slightly wider than one might initially think.
To half-answer my own question from earlier, there are a number of mobile SoC that clock one core higher than the rest, though I haven't been able to figure out if there's a downside to it (for example, are they still able to share cache with the other cores?). So if anyone believes that 4 cores at 2Ghz is possible, I think it should be made clear that for the same battery life you can get six cores at 1.4Ghz, along with one core at 1Ghz and one core at 2Ghz, for almost the same total power budget, I think it'd be six percent higher or something minor like that. The only downsides are die size and if your code benefits from just a handful of heavy threads.
If a game is engineered to run several threads really fast, then 4@2Ghz might be preferable. But if it relies on just one thread going fast, or if it's processes are modular enough to run in parallel (which is growing more and more common it seems, but I admit I'm on the outside looking in), then the system I laid out above would be more effective.
As for die size: According to this post from last November
So I was bored and was playing around with a new app I got on my iPad...
Basically just scaled the die shot to come out to ~460mm2, then got the rest from there, about ~4mm2 for the A78AEs (so of course ~48mm2 for the x12 cluster of them). Course it's all an in exact science based off a jpeg, like depending how it was cropped and how they're counting the size would mess with all those measurements.
A78AE cores are around 4mm2 on Samsung 8N. I don't know how accurate it is, but I think it's safe to say it's in the ballpark. So at worst 8 cores would add 16mm2 over 4 cores. But I've read that A78AE is larger than A78C, and 8N is the worst case scenario node for Drake, so I would not be surprised if the actual difference between four and eight cores ends up being ten square millimeters or under, maybe as little as 6mm2 added onto the die. Which isn't nothing, but it isn't much either. If Nintendo okayed 12SM, I can't imagine this would be too much for them.
EDIT:
@oldpuck "One of the big wins of the Switch was it’s flat architecture. I suspect they won’t want to make it very difficult to optimize for Drake"
That's a good point I hadn't considered. I can imagine the whole industry learned from the PS3 that power is useless if there's too much complexity in the way of using it. Granted this wouldn't be anywhere near as complex as that, but I think simplicity winning out is far more likely than my post implies.