Shulker Preview

Shulker Preview is a client-side mod that lets you open a shulker without placing it (however, you can't take the items it contains).
The button to view the contents of the shulker can be changed from the game options.

Here is a demo :

As of version 1.1, you can also open shulkers in inventory and containers by right-clicking.

Each shulker color has its own display :