No doubt now that I have committed this thought to print I will be proven wrong, but I get the impression that nobody writing for DW outside of Big Finish has any interest in revisiting Susan or how the Doctor came to be a grandparent.
(Next week: RTD announces season-long plot based around Susan and her parents)
I actually think bringing Carole Anne Ford back, and possibly regenerating her on screen, would be the simplest and best way to make the ‘Anniversary Specials’ actually be anniversary specials, and not just a mulligan on an ending for Donna RTD regrets, and a way for the show to get a reset back to ‘the popular doctor’.