I think we will continue to see Catherine wearing "significant" pieces from HM's famous "Vault". Camilla has some amazing pieces and, should she need more, I am sure she could have them, but I believe there is something more behind the loans than the jewellery itself.
Firstly, I think the Queen gets a kick out of seeing Catherine wearing the same sort of great jewellery that she herself wore when she was young. If you track Catherine's jewellery something else pops up immediately and that is that as she has grown more self-assured and confident we have seen the type of jewels she wears in the evening change.
The first pieces HM lent her she wore with her hair down and all we could see was hair tangled in chandelier earrings and tangled and almost obscured the necklace. Her evening dresses were not "gown" and didn't lend themselves to being accessorised by historic jewels, however, over time we ended up with Catherine's last State Banquet and her gown was quite dramatic, almost theatrically so, and she looked totally at ease with a kings ransom on her head and around her neck and wrist.
When you look back at Catherine's evening gowns you can see the evolution of a future Princess of Wales. Her dresses turned to gowns and if we know that if she should choose to wear her hair down, it would not be tangled in nor obscured by her hair. She holds her head a little higher and stands a little straighter these days and the Queen is loving it.