Having spoken to some of the decision makers in BA, I can tell you they don't honestly know what they're going to do. A month ago there was going to be no external recruitment onto the 747 - now it's open. It's a very fluid situation and they change their minds VERY frequently. All I can say is keep an eye on the recruitment website and here. If the requirements change, you won't need to ask, someone will post here in a matter of minutes!
The opinions of most managers seem to be that there will most likely be recruitment of non-TR'd/military/SSPs again - when? - no idea.
They have even mentioned a pre-selected training scheme (they select you, you pay for your training), but again, these are just rumours.
Part of the issue is the length of time people can spend in the hold pool - 12 months. What they don't want to do is recruit loads of people into the hold pool and then find they don't have the training capacity to offer them jobs before they expire. Logically I'd suppose they'll exhaust the supply of TR'd applicants first before widening their net. As has been mentioned elsewhere, it may not take that long to exhaust the supply of TR'd 747 applicants - based on current selection success rates they'll need 300 applicants to get 30 successful ones.
It really is very complex, predicting what will happen is certainly beyond me!