A friend of mine told me about the switch layer in Anime Studio. I’ve looked into Synfig and haven’t found anything like that.
There is a PasteCanvas layer in Synfig, which is very close to Switch Layer, but it’s displays all child layers at once. Then a wild idea came into my mind: what if we allow user to define a range of visible child layers? Each layer have a “Z-depth” parameter, which defines layers order. We could limit layers visibility by adding “Z-depth limit” to PasteCanvas. Animating Z-depth limit could give switch effect… and much more cool effects if we will make range boundaries “fuzzy”. I.e. when layer have z-depth which is close to visible range, it’s appears semi-transparent. Sounds funny.I want to dig that someday.