Thanks Iain, as I thought really.
I had a question buried in the bottom of the post about adding tracks inside the loop whilst still using all the RD5013 features.
This revision is a hybrid of the first one, adding in some storage sidings inside the loop (but not inside the switched reversing section itself).
So the loop is basically the same as in the RD5013 documentation on page 27 where it is section 5.3 "DR5013 with sensor tracks (S0, S1, S2, S3) and LocoNet" with some added storage tracks:
I was thinking of using more of the unused YD6016LN-RC to also report back on the occupancy of the additional storage. They are not in the reversing section, but are in the sensing blocks.
Here is the revised track plan:

Forget the outer double tracks.
All the yard tracks, storage, and reversing loop are on one booster.
So S0, S1, S2, and S3 are the tracks at the ends of the reversing loop (the inner curve). Please excuse the blurred image. The additional storage tracks are added in next to the loop switch. I hope that's clear.
Is it possible that I can have all the RD5013 features and still have some extra storage inside?
All the examples of how to make reversing loops never mention trackage inside the loop. I've not actually got the hardware so I can't test it for myself.