The series made the jump from BBC Two in Season 2, BBC One in Season 3, then finally there was a co-production between BBC One and Starz for Season 4, which was re-titled Torchwood: Miracle Day.
Should the series return, I’m sure there would be many options for a network to take it.
BBC Three is an option for the return, but certainly not the only one.
This is especially true in regards to the revival happening on BBC Three, which, as mentioned previously, was only one of the networks to air Torchwood.