copy/paste to other project
You copy the layers or folders you want, then close the project and open another one and paste them in.
This causes all sorts of issues and cannot be supported.
Then figure out how to make it not cause all sorts of issues. This is a lazy, BS response. All you need to do is make it package a pseudo-smart layer up into the clipboard.
Thomas Briggs 0 commented
There are times I've had to rebuild a file because some element is corrupted but the other 10 layers are fine. It's a total pain to rebuild perfectly functioning layers.
YES YES YES! I have tried this several times without luck when having two versions of SP open at the same time. It's so disappointing that it wont work, I dont always want to create a smart material to clutter up my shelf.
You can pretty much already do this with creating smart materials.