I don't think there is enough evidence at present to either support his intruder story or to denounce it. The truth may well be far removed from either version.
Many people working on the assumption that OP killed RS in the bathroom intentionally are still going along with the theory that she'd gone to the toilet or had fled knowing about the gun. Premediation doesn't mean he planned it weeks in advance.
It's not beyond the realms of possiblity that she locked herself in to avoid a verbal argument and his frustration led him to act first and regret it as soon as the shots were fired. On the other hand if you are terrified that someone is in your house, waiting to shoot you dead in your sleep, you may well feel that you are going to 'kill or be killed'.
The problems I have with the defence so far are the fact the balcony doors were open while he dozed, doesn't fit the paranoia image, the attempts to get stuff out of the safe, the denial of a house in Italy which was technically true but failed to mention his access to this house and the positions of the telephones. I believe that someone living in SA can be scared enough to shoot through a closed door, based on what has been said on these threads but I still cannot get my head 'round him not stopping to touch her and say 'stay here' or 'don't get up we've an intruder' (and finding she was gone).
If she was in a guest room or living room I could see this happening but not when they've been asleep in the same room.
I feel dirty speculating though and I don't know how much of the bail hearing we should see/hear because it leads to these papges of us playing Miss Marple as has been said.
Phone records and ballistics should be the key here.