That's so last year.
That news has past its sell-by date.
That news is already being used to wrap chips.
You don't say.
I'd never have known.
Tell me something I don't know.
Sometimes people just say 'Gosh' (itself rather a dated word, and they hope the 'oldness' will rub off.)
But there are lots of options - as laboured as you like. 'Did the newspapers have pictures in those days' - not an idiom, but the sort of thing commonly served with sarcasm.
And, on the subject of service, I've heard tennis commentators say things like 'The man who told you that - was he still playing with a wooden racket?'
Interested in Language