Has there been any reference or things in the background relating to Bad Wolf since series 5?

No, thank God.

The prisoner Zero bloke in Eleventh Hour had a bad wolf. Bad to the bone.

She scattered "Bad Wolf" all over space and time, seems funny it hasn't popped up for a while.

Must have fallen down the cracks.

to lead herself to Satelite 5 no one else it was kind of finsihed and on a loop in her timeline somewhere who knows Timey Wimey remember