There are Intel CPUs which come with bundled RAM. For example Intel Core Ultra 5 238V. It's like SoM: RAM is mounted directly on the CPU package, not even soldered on the motherboard. I'm not sure what particular advantages does that bring over traditional packaging, maybe shorter wires to allow for faster turnarounds between CPU and RAM. But there's zero chance of upgrading or replacing RAM for sure.
In theory, but that is not the case with Lunar Lake, which nowadays does not have a greater bandwidth than the current CPUs with external LPDDR memory.
However, at launch, a year and a half ago, it had a bandwidth about 15% higher than competing CPUs.
For a really "massive increase in bandwidth", it would have needed a wider memory interface, like AMD Ryzen Max, which has a 256-bit memory interface, instead of the 128-bit memory interface of most Intel/AMD laptop CPUs.
Yes, totally. By introduced I didn't mean they were the first in the space but rather they have introduced it to the laptops they're shipping now. But yes, it's been a thing for awhile on other architectures as well.