It took quite some time to validate the news and now I can certainly say that the future generation 2005 product is codenamed Fudo. Last time, the R420 was codenamed Loki and ATI was terrified to learn the fact that we knew about it.Source: The Inquirer
R520 is the next chip that will come after R480 Q4 speed update of R420/423 marchitecture and it will represent the chip with new features with at least Shader model 3.0 support if not even more advanced – I mean programmable shader model. I guess it won't be just re-named R400 as it has to add some more features to compete with Nvidia's NV50.
ATI's R520 codenamed Fudo

ATI's R520 graphics core is codenamed 'Fudo', according to the Inquirer.