I believe this is the first time has ever advertised RAM in an iPad or iPhone.

Also the first time they shipped different amounts of ram stratified by storage choice.

They did do it before, but it wasn't advertised.

I'm pretty sure the 2018 iPad Pro with 1 TB also had more RAM than the other models.

It had 6gb of ram but only 4 was available to apps. The extra 2 went to multitasking.

Configurations are expensive. If you have 2 RAM configs and 4 storage configs you have 10 different models. This way they only have 5 models.

Does anyone know what the reason for this might be? (doubling the RAM because the SSD is larger)

Also are there any performance implications to this? Should I get the 1TB version for the 16GB RAM because it'll be a snappier machine and more future-proofed?

Its to reduce the number of SKUs they have. Its common for hardware to have only the high end specs matched with other high end specs because its not often someone wants the absolute best of one spec and the worst of another spec.

If they as others have suggested include a hypervisor that would allow MacOS to run on it, not only would they probably sell out overnight, but it would require more RAM.