Halo: The Master Chief Collection's development is continuing a-pace, which aims to update several classic games in the series and bring them to the PC platform. One of the next updates to be brought to PC will be Forge mode for Halo: Reach, something that is currently conspicuous by it's absence.

The mode will also appear in future games to be released in the collection, although the timeline for that is currently unclear. 343 Industries have said however that it is currently making "great progress" on Forge and that it is working in implementing PC specific functions for the mode. They also released this screenshot from the mode to whet your appetite;

343 also posted in the update that the update will have;

• Support for mouse and keyboard controls for all functions of Forge and Theater.
•  Support for in-game HUDs of Forge and Theater to support mouse clicks, selection, and keyboard shortcut keys. 
•  Support for Forge and Theater settings in pause menu and front end.
•  Forge and Theater support for video, audio, and other settings for each game as selected in the front end.
•  Support for placing and manipulating all Forge objects via mouse and keyboard.
•  Support file saves MVars/GVars saving and uploading to Xforge.
•  Forge and Theater modes respond appropriately to Windows events such as resizing, minimizing, switching to full screen and windowed, etc.

You'll also be able to have more objects on the new PC version compared to those seen on console releases. 

You can read the full development update here.