It is not as surprising that modern chips stack or tile dies together, such as on phones and the like.
edit: Note also there is historical precedent for specialized SoCs that integrate DRAM on the same ASIC, see eDRAM: https://en.wikipedia.org/wiki/EDRAM
Your argument also require the reader knowing the technical premises that CPU and RAM processes are different nm, and that processes of different nm cannot be done on the same chip. These are not obvious or even absolute facts to anyone.
Actually a good place to find these sorts of citations are tech magazines that explain these new things, maybe like Ars Technica used to (i.e., a piece on "What is Apple's unified memory"), or else in academic research that sometimes studies contemporary chips, their research papers might have a blurb discussing the actual hardware architecture of such and such company's design. Or maybe there's an EETimes piece discussing Apple Silicon technology in one of their back issues, e.g. in trade journal literature.
So, what is well known varies depending on the audience. It is both plausible, and appropriate, for technological ambiguities and details to be explicitly discussed and clarified, either by the maker or by other journalists and writers.
And finally, consider also what is well-misknown. If you go online and look, lots of lay comments since Apple Silicon really do believe they are literally the same IC chip. So you have to ask how did that come to be?
Unified memory has nothing to do with them being on the same chip… it just has to do with them being the same pool of memory shared between cpu and gpu. Apple marketing is pretty clear on that too. The only reason it’s unique is that doing unified memory on laptops is kinda unheard of until then. It’s been the standard on tablets and phones for years.
So one day, when we have process nodes far smaller what we do today, a DRAM fab can print highly complex patterning for logic, compatible to today’s CPUs on die. And the logic fabs will be making cpus many times more complex than that. Because economics.
Logic processes do not have the capabilities to even manufacture DRAM. It’s not about cost or yield, they just do not have the correct blocks to make DRAM. The processing to make DRAM makes it incompatible with making logic at the current speeds and densities.
There were some much older processes where you could do both, but those are about 10 years old now and we’ve long since moved on. I do not think there will be a future where you can do both.
And looking closely is that some kind of mounting bracket? They look like metal handles surrounding the square area.