Embarcadero has not included the MDI Application type in FireMonkey because it can not be converted to Mac OS or iOS. Delphi and C++Builder are still 99% Win32 so all MDI Apps have to be redesigned to be converted to FireMonkey.
I would like to see a Form Management System for the Win32 FireMonkey that will keep track of the Main Application Form and Workspace Forms too replace the MDI Application style. This should provide the same ability as the MDI Application style allowing us to identify the Active Workspace Form, for loop through a list of all Workspace Forms, keep the Main Application Form separate from the Workspace Forms. I am there is more to the MDI App style that I am not remembering. This will allow Win32 programs the ability to convert our apps to FireMonkey without a complete redesign. I personally don’t care about converting to Mac OS I need this for Win32. If it can convert to Mac OS also, well that is great too but not necessary.