With the new feature open document as floating popup available in Univeral Gui, it's nice to follow it up with another option to emulate lookup popups. 

The reason for that is in lookup popups, when it's opened it's the only focus of the page. Other components are un interactable, hence the grey background. Making the page opened needs precedence and attention from the user. 

While in the current one is that users can still interact with other components of the page. I understand that the choice was made because opening a page is the output of the process and lookup pop ups are pages opened while being inside a process like editing or adding a record.