One partial way to do this today could be to create an “on holiday” group, set it to Automatically set as primary group, and give it flair and title?
If you’re going away you can join the group, when you’re back you leave it. You’d also be able to see a list of who is currently away by visiting /groups/on-holiday.
The biggest missing piece would be mentions, but the flair/title would be visible on your profile and on any of your posts.
This would be more for internal communities than anything public-facing… for public-facing communities some sort of “who else should I contact” auto-response feature might be necessary.