I use goodnotes exclusively when I am designing buildings and putting objects on layers would be such a useful feature

I use goodnotes for sketching and layers would enhance the product a great deal

Add a lock text/drawing feature so that you can selectively not erase it (i.e. Lock it, write over it and be able to erase only what you wrote over it.)

I am a teacher and give live presentations multiple times, and reuse year after year. Transparencies would be amazingly great. Now I have to go back with my eraser and carefully erase changes to each page between class periods. Not simple, fast or efficient.

I use this app for my sketching my architectural designs and the ability to work in layers would be so helpful. Rotating hand drawn notes/sketches would also very nice. If these features are too specialize for most people Goodnotes may want to consider selling these features as an optional add-on. This is by far my favorite app.

Yes and the ability to order them like "send to back" and "bring on top"

As well as scaling and rotating the layer...