There’s lots to explore there. The station outside of space and time. Between universes. Having the doctor bump into unknown incarnations of himself knowing or unknowing. Hell, have himb end up being the catalyst for what sent his past self on the path out of time lord society. Heck, a modern reintroduction and exploration of the time Lords themselves. At least for narrative purposes. Bigger meatier things to really sink into story-wise.

The doctor’s not supposed to cross his own timeline. How can you really do that if you don’t know it. Have him land someplace and get tossed into a crisis as is Doctor Who tradition. Over the course of four episodes have an arc where he meets and is forced to Ally with someone equally is brilliant as himself. But much more morally Gray and willing to use violence. They Clash But ultimately cooperate to save the day. As they are both preparing to part ways. The doctor opens coms and says by the way I didn’t happen to get your name. To which the other replies the doctor. Followed by silent Tardis scraping noises. Dun dun dun, theme song swells. And there’s so many different ways to take it from there.