Originally Posted by Black Guardian:
“What do you think he was inferring Den? As far as we know there was only one thing lurking at the heart of the TARDIS.”
I'm not entirely sure - shall we have some fun speculating?
1. The Master - in a controversial scene was last seen disappearing into the heart of the Tardis, accompanied by a loud burp.
So I suppose it could be him - although RTD has said a few times that it's too early to bring him back.
2. The Gelth - spoilers seem to suggest they are set to make a return in series two. The Doctor defeated them as they attempted to cross over via the rift - weren't they dwelling in the vortex in some way, or is my memory playing tricks on me?
The only problem I have with the Gelth hitching a ride aboard the Doctor's body is that they manifested as blue light rather than golden when they appeared to us.
3. I can't help thinking about a point you made during series one, i.e. that a race as poweful as the timelords would have had some kind of disaster recovery or backup plan in the event that their race was destroyed. Makes perfect sense to me.