Looks like the rumors for N31 are corralling on the new theory that it's a single N5 GCD and all the Infinity Cache and memory controllers are on N6 MCDs (6 total). Still MCM architecture, probably uses fan out bridges, but not 3D stacked. Still, with all of the logic on N5 and all of the IO and cache on N6, it appears to be very cost optimized. The N5 GCD likely is only around 400mm2 knowing that N21 was 520mm2 and around half of that was shaders. 520mm2 / 2 * 2.4x shader count / 2x node shrink gives you around 315mm2. Add on the PHY for the fan out bridges and extra die space for better RT and architectural improvements, 400mm2 seems to be within the ballpark.
There's probably other shrinks elsewhere. Missing backwards compat for deprecated features like the old geo pipeline, more SIMD32 versus work dispatch, etc. Arch improvements so far seem more about fixing old problems like needing to decompress in certain stages; and the improved RT pipe that was patented a while ago used the texturing units, meaning any expansion there is probably minimal. Bridge is also pretty minimal afaik, could see the chip end up in the mid 300mm range.
With the price hike from TSMC and extra dies a single 128 simd32 compute chip alongside bus and etc. probably costs a bit more to produce than the 6700xt. Thus my guess of $500 for a full chip and $400 for a partially disabled/binned (non "xt") version. Of course if things go bad those prices could rise by $50-60 or so
Hopefully though it'll be a bit smaller, and that price increase won't happen. It'd be real nice to see 6800(non xt) or a bit better at $400.
Edit- really though I don't understand the rumored specs entirely. The most logical compute tile should be like, 96simds (48 RDNA2 compute units). The cost would be tiny, probably as low as a Navi 23 (6600) board for each compute die. You could pair it with 128bit/256bit/etc. bus and SRAM as you scale up to 1/2/3/4 compute dies. A single one would be theoretically 20% faster than a 6750xt at minimum, and more for raytracing. That should be the sweet spot for cost/performance right? Eg 12 teraflops/8gb for $329; 15tf/16gb $400; 24tf/16gb $700; 30tf/16gb $1000; 36 tf/12gb $1250; 44tf/24gb $1600; 58tf/16gb $2500.