WG game set in SCP universe would be interesting. There’s a ton of interesting characters to work with (such as 999, Dr.Bright) and you can even come up with your own SCPs.
The plot wouldn’t have to be about any containment breach, but maybe just life in facility?
You can be a scientist, or D-Class personnel (or maybe Guard?)
Mod for an already existing game would be hard to make, so it would either be a visual story, text adventure or an interactive novel. Whatever floats anyone’s boat.
edit: here are some of my ideas:
SCP-999 (the friendly slime) making you gain weight
SCP-294 (the drink machine) giving you weight gain liquids
SCP-049 (the medieval doctor) giving you weight gain serum
SCP-1025 (the disease book) making you gain weight through some illness
SCP-914 (the upgrader) making you fat through upgrades (maybe The Fattener instead of The Upgrader?)
SCP-871 (the infinite cake) cake that reappears at different forms or sizes