If it had gone to series, there's an amusing detail on the TARDIS console destination panel (the design drawings for which are printed in Gary Russell's book), which means the show might have been somewhat restricted in the times and places it could visit.
The wooden destination tumbler has a choice of six options: 'Argolis' , 'Calufrax', 'Gallifrey', 'Earth', 'Manussa' and 'Sarn'...
Similarly, the only years available are '5725.1', '5725.2', '5725.3', '1998', '1999' and '2000'.
The only dates available are from December 29th to January 3 inclusive.
So if you wanted to visit Tara (and why not, it's a lovely planet!) on 15th March 2008, you'd be buggered!