I was testing out the new /place command when I noticed only 2 structures could be placed. minecraft:trail_ruins and minecraft:trial_chambers.
You can reproduce this by typing the following in the chat and commands:
/place structure (make sure to add a space after structure)
I am not sure if this is intentional or if I am missing something, but this is all I know.
This issue is being tracked at MCPE-188512.