http://www.scp-wiki.net/scp-278
I'm suggesting this SCP because it might be able to play some roles in the game. I have been able to come up with a couple uses that I hope Regalis will look into.
1) A third exit/ending (Gate C) is added into the game where SCP-079 manages to insert itself into SCP-278's system and take control of it. SCP-079 then proceeds to use the machine to escape the facility through Gate C, where MTF units and helicopters have already been stationed. As the SCP forces open fire on 278 and 079, the player witnesses the events as he/she attempts to sneak away and escape, only to be killed by an MTF, helicopter, or, if it is re-inserted in the way that another user said once before, 513-1, where it appears before him/her and the screen goes black. In the ending audio, it is mentioned that SCP-079 failed to escape and SCP-278 has been destroyed, and the Foundation will proceed to contain the SCP's within the facility.
2) The player uses SCP-278 to escape the facility, through a third exit. (Gate C, once again.) (On a side note, SCP-682 can possibly chase the player in a chase scene, as Regalis once said.) The player attempts to evade MTF units that open fire and try to kill him/her. If the player dies, he/she wins the game in a bad ending case. If the player escapes the MTF units and/or SCP-682, he/she will be intercepted by the Chaos Insurgency, AKA the mysterious figures that are seen in the Gate A ending, and is taken away, in a somewhat good ending case.
I would have suggested this long ago, but I forgot the SCP number. Commentary welcome.