For science...you monster
This mod is installing as I write. Thinking With Time Machine creates an alternate (if somewhat crushing) epilogue for Portal 2, putting Chell right back in the lab. Her free hand's now holding a time travel tablet, which makes it possible for her to weigh down plates, line up portals, and hand off cubes to her temporal twin. It's like Braid, but...with Portal. Two great tastes that taste great together, I bet.
Excited as I am to take this for a spin, I can feel myself preemptively designating this experience as something akin to AU fanfic. Nothing could convince me that anything but this happened after the main game ended.