People who played the Portal games might be well-versed in Portal 2 and remember the Perpetual Testing Initiative, which still exists. People still play the various custom test chambers that have either been created using the Hammer tool or the built-in modifications to the game. And there have been crossovers between G4 MLP with the games, and Steven Universe with the games. Let's not forget Lego Dimensions.
With this in mind, yet another time, imagine The Loud House and The Casagrandes, modern animated Disney shows, Syfyman's versions of Smoking Wrecker's custom Mako Trio and Jerry Owens, the Kraekkarians, the werewolves and non-werewolves from Shadows of Love, the Blood Brothers and their friends and families(Eric, Dylan, Rebecca, Naomi, etc.), the merfolk and human friends from Power of Water, my TTS characters, various OCs, you name it all inhabiting the same world together, or maybe different worlds that can be traversed.
Whatever the case, there could be multiple testing facilities that Aperture Science would somehow be able to build, with each would having more than one facility. If it was one world that they were all inhabiting, there could be multiple facilities or just that main one, with them being tested by GLaDOS. Maybe they could be designing chambers alongside her. Hopefully, it wouldn't be too much like this video by Mochirisu about his Microsoft Sam working for GLaDOS, though we could keep true to GLaDOS's original character and development. Plus, imagine various main characters of those mentioned franchises, and whoever is nerdy(Lincoln, Ronnie Anne(maybe), Marcy, maybe Libby, I guess Tater?, etc.) designing custom test chambers for GLaDOS, and maybe creating new Aperture products. Or they're creating test chambers for the Steam community.
A YouTuber known as Demon Arisen posted videos explaining the design process he goes by, classifying varying test elements as core components and the rest as supplements.
There are several videos, three of which are by Duncan Jones from the Yogscast, that showcase the process of designs using the plain version of the system. They could serve as inspiration for whatever ideas those characters as mentioned earlier could think up for test chambers. And I wonder if anyone could think of ideas for who could play those chambers. As for the designers, I hope they know what is worth avoiding for creating test chambers.
I actually built a forum to collect responses for ideas that people might have for test chambers for me to create. I decided recently to copy that forum to see who might have ideas for which character of their choosing could think of which ideas they might have for test chambers. Maybe they could listen to ideas from others and built chambers based on them. A lot to think about.