Link: https://www.gamesradar.com/games/fps/doom-the-dark-ages-dlc-is-freaking-huge-says-director-its-basically-like-a-sequel/

In other words, "it's massive"

So, an expansion pack...

Adding a dash mechanic would appeal to all the Doom Eternal fanboys

How expansion packs used to be. The last game I saw get a DLC that basically added twice as much game to the game was Shadow of the Erdtree and before that, was probably sometime back in the early 2000s before Oblivion released the Horse Armor.

Horse armor was the Harambe of video games.

The Horse armor basically doubled the games content. It was a truly magical moment.

Monster Hunter World: Iceborn from 2019 / 2020 also doubled the game content.

The horse armor playthrough was functionally a different game. Each armor was like a new lens through which to view Cyrodiil.

If it makes you feel better the Horse Armour killed the series as they only ever released one game after it.

Obviously a very different kind of game but the Factorio Space Age DLC more than doubled my play time in the game and imo is one of the best DLC value-wise that I've ever purchased.