No, I don't think it's new at all. From Ian McDonald's site, Working more productively with bash 2.x/3.x[1]:
> A relatively new feature in bash is programmable completion, which has been available since the beta version of 2.04.
Taking a quick look at Bash's official downloads site[2], Bash 2.04 was released in March of 2000.
[1]: http://www.caliban.org/bash/
[2]: http://ftp.gnu.org/gnu/bash/