I'll add this for memory subsystem reference. Currently the Switch uses LPDDR4 at a maximum of 3200MT per second docked for a maximum nominal bandwidth of 25.6GB/s.
If they use the same 64-bit interface but at LPDDR4x speeds: 4266MT/s => 34.1GB/s
64-bit interface updated to LPDDR5: 6400MT/s => 51.2GB/s
Using a 64-bit interface to LPDDR5 brings some LPDDR5 inherent advantages to the table as well, so the improvement would arguably be somewhat more than what the numbers suggest.
8GB LPDDR5 would be a single package.
Of course, Nintendo could be ambitious and double the memory interface. In which case:
LPDDR4x: 4266MT/s => 68.2GB/s nominal
LPDDR5: 6400MT/s => 102.4GB/s nominal
But without even getting into the thorny discussion about what is a good idea or indeed possible at 4k resolution and 10W at Samsung 8nm, we can see that the memory subsystem variance is HUGE!
Of course, the bandwidth needs are dependent on what you try to achieve, but it has been pointed out as a main bottleneck for many Switch titles.
On the other hand, how much can happen performance wise within the current Switch power envelope? (Should we use the original Switch model instead?)
Then we proceed to compare process technologies. Under optimal circumstances TSMC 10nm (which is similar to Samsung 8nm) is twice as dense, but doesn't offer twice the power efficiency vs. Mariko 16nm. Lets assume Samsung 8nm is better, and can offer both twice the density and twice the power efficiency. That would imply that if we could afford roughly the same die size, we could squeeze in twice as many transistors, which, when clocked the same as current models would consume roughly the same amount of energy. Assuming a bit of increased efficiency, we would also need to provide at least twice the bandwidth for the SoC not to be more hamstrung by bandwidth than the current models. Which fits neatly with a single 8GB LPDDR5 module.
This kind of Napkin Math always pegged an updated Switch at roughly 2.5x the performance of the current model. But without actually knowing neither the memory subsystem choices nor (yet) the process technology, the span is huge. Nintendo may go really cheap with the memory and opt for 64-bit LPDDR4x (ack! pfft!), or they may be really ambitious and feed it via 128bits worth of LPDDR5, and fab on Samsung 5nm. And I'm starting to feel that these critical parameters won't be known until after the device is launched making literally writing a Bible sized thread filled with speculation is a wonderful commentary on how public tech forums work. It is actually to the credit for B3D not to have engaged in this, but honestly, I mostly feel that this may be because the more prolific residents here would prefer to deny the Switches existence outright.