343 is trying to revive Halo 2's infamous 'Earth City' E3 demo

pcgamer.com:

Halo has taken many forms throughout the years, and left scraps of those development paths going all the way back to when it was supposed to be an RTS on Mac. This week, Halo caretaker 343 Industries announced a massive project to pick up those scraps, working with modders to bring cut content back into The Master Chief Collection.

In a beefy blog post titled Cutting Room Floor(opens in new tab), 343 revealed that a secret «Digsite» project has been working on not only collating cut content, but fixing up half-finished assets to make them work within the current Halo MCC entries. While 343 won't say who its working with or how they were selected, it's split Digsite into two teams—Digsite Alpha for pre-release Halo: Combat Evolved content, and Digsite Delta for Halo 2 development scraps.

Between the two, the cut content includes scrapped Halo 1 vehicles like the Spectre and Kestrel; old Master Chief models from the game's RTS roots; previously-unseen NPCs, levels and weapons; and a teeny tiny Warthog called the «Piglet». But it also plans on making a notorious part of franchise history, Halo 2's famously impractical «Earth City» E3 2003 demo, playable for the first time ever.

If you're old enough to remember Halo 2's stunning gameplay debut, you'll mind that it sported some then-cutting edge lighting techniques that never made it to the final game. A 2018 Digital Foundry video(opens in new tab) dove into how exactly the Earth City was accomplished, but in short, Bungie used a whole load of smoke and mirrors to achieve effects in the demo that turned out impossible to expand into a full game. 

I can confirm we are working on a rebuild of the original E3 Earthcity scenario that makes it playable in modern retail Halo 2,"