I would hazard a guess that if the Torchwood of Pete's World was able to develop technology capable of traveling alternate realities then there would be no reason to stop Rose and her Doctor from doing so should they want. Starkers does have a point...why would they want to? I suppose that the original intent to develop such a technology would be so Rose could attempt to travel to her home reality but finding it still locked off decides to finally accept her fate with the Human Doctor and they travel through time. I'd be interested in reading your fic EJA if you ever write it.