Who is the indicator for though? Wouldn't users of that language quickly come to expect that inactive is not necessarily dead or useless? (Especially with Common Lisp, stuff decades old is still useful.) And I find outsiders unlikely to care that much, it's just a nit random passerbys will make when they think they need to comment on something, rather than actually informing a serious decision.
It's also kind of pointless to "update the copyright year" for individual works tied to your name, since the copyright lasts x years after your death. If anonymous/pseudonymous, then it's like 95 years after initial publication date, and you can't just extend that arbitrarily by updating the base year and nothing else every year..