Okay, hear me out. Next episode’s name is “The Five Companions”.
Follows directly after RW and regeneration doesn’t end with Billie who actually plays Rose in this. In some way, she splits in too Rose, Amy, Clara, Yas, and Ruby. And it is just a weird episode set in the TARDIS where the companions try to find out how to save the Doctor. Ends by them finding Susan who helps them to save the Doctor but in doing that regenerates. The companions end up in their own timestreams except for the second Susan who becomes the next Doctor’s first companion.
The problem is probably that the Doctor got stuck in the TARDIS when he pour himself in to it and The TARDIS brought who she thinks can help.
This might fit better in Doctor Who Dreams but I think it could be fun 