DenOfGeek seems to think what we know about the Xmas story hints at a loose adaptation of RTD's novel
Damaged Goods. I say loose as I can't imagine someone getting a blowjob in a taxi at 6:30pm on BBC1. He'd also need to tone down some of the scenes of racism, homophobia, violence, etc.
https://www.denofgeek.com/tv/doctor...link-to-cult-favourite-russell-t-davies-book/
Interestingly, I didn't know until reading the article that RTD stopped a reprint run of the book in the lead-up to the 2005 revival, because he didn't want people getting the wrong idea about what the show would be like. Though the original story would fit perfectly with Torchwood.