Totally and earnestly clutching at as many straws as possible rn, however desperately, but the above is taken from the Next Time trailer for ‘The Doctor Falls’ as seen at the end of ep 11. I could be entirely wrong, but that looks very very much like Bill’s hair and silhouette walking upstairs behind Nardole. (the silhouette of her costume very much looks like the bulky torn grey coat she wears at the end of episode 11 too, complete with fraying fabric at the bottom!)
A closer look:
I’m perhaps taking obsessive trailer sleuthing to a whole new level, but it’s all in the name of peace of mind so it’s worth it! Tell me that doesn’t look like Bill?!