Silicon in general is a pretty good heat conductor, so that's not a huge issue. Jacking up density does mean you get more heat in the same area, so you do run

Silicon in general is a pretty good heat conductor, so that's not a huge issue. Jacking up density does mean you get more heat in the same area, so you do run into issues with that. That said, having dies close to each other dimensionally is good, since you run into issues with latency if stuff is too far apart. Speed of light is actually a limiting factor. So, although you can't have all of the silicon 'hot', you can increase the amount of silicon you have as long as more of it is 'dark' (i.e. not active). Seems like this is a benefit overall, although I wonder if the cost is actually effective. Even processors today do this - if they're computing complex instructions (e.g., AVX512), they actually downclock because too much silicon is used and they would heat up too much otherwise.