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I think that the show should not continue filming, especially not with Katy Manning, who is far too old for this. The only companion that I can possibly see is Ace, who has a lot in common with Clyde.
If they wanted to be really great, I think that Daniel Anthony and Anjli Mohindra should be offered jobs on DW if they want, starting with Series 8 as 7 is likely being planned/written now. I exclude Tommy Knight because he has retired from acting already.