I'm not currently flying weighshift, but was flying both for about 8 years, and hope to start flying weightshift again sometime soon.
They are TOO different to confuse, once I had around 20hrs total on weightshift, it was no more a problem than say confusing my car and bicycle controls.
I'm more worried switching between 3-axis microlights and SEP, because they look and feel similar, but need quite different attitudes, speeds and flare heights.
G