[Macha]

Even a restricted NAT should allow for this without explicit port forwarding configuration?

Unless you're doing something like active FTP where it's replying to a different port than the one the request originated from. Which would be a interesting choice for a console designed in like 2018.

[laumars]

It’s a firewall thing not a batting thing. You need a stateful firewall to do that kind of smart port forwarding. Which, to be fair, all consumer routers should have.

Stateless firewalls, however, need to have explicit rules for UDP traffic. So that’s what Nintendo are addressing here.

[fulafel]

NAT functionality especially for UDP can be incredibly flaky in a lot of consumer hardware, mangling payloads, randomly dropping associations or having extremely short timeouts, and other plain buggy behaviour.