Huw has said that it does look as if only one line will be used into Monument. Indeed there isn't a signal at the eastern end of Monument platform 4, although IIRC there is a Stop sign with 'Contact Control', similar to some other locations where a reversal could be made with permission from South Gosforth. There are signals at each end of the platforms at Manors, so again that wouldn't be a problem.
As far as I'm aware the only time Manors platform 1 has the wrong-direction movement is when the empty stock is going back to the depot. I've never heard of anything else being terminated at Manors plt 1 and going back out towards Byker, as it could be terminated at platform 2 and sent back over the diamond crossovers.
I've done a bit more thinking and now I can remember two occasions where a wrong-line movement has been done into platform 3 at Monument. One morning last year I was waiting for a train to Monument and there'd been disruption due to a train being withdrawn from service. An announcement was done on the PA telling us to go from platform 2 to 1 at Manors, as the next train was coming in the wrong way. Of course when we'd went over to platform 1, it changed and reverted back to platform 2. So, although rare, it does happen. I'm sure there will be a few of the more well-known faces out to get a video of it happening.
Next weekend should also see the return of the wrong-line movement from Manors to Byker, as the line is shut between Byker and North Shields. I've also had word that Gosforth South Junction is being replaced later on in the year over a period of 5 days, which should mean that the depot avoiding line is brought into use.