Seems weird that they didn't do a report on Nintendo, who overall had the most screen time and more than enough games and presenters, to judge.
Nintendo
Treehouse cast is pretty diverse overall and the majority of segments had a female presenter (although the absence of Chiko whose destructive tendencies were a lot of fun last E3 was definitely missed). Unfortunately all of the developers, Japanese and otherwise, they had on were men.
2 Metroid games, both presumably with Samus Aran, white woman as protagonist.
Pokemon UltraSun/UltraMoon showed both male/female player characters in trailer, both white.
Mario+Rabbids, only white humans shown
Super Mario Odyssey, humans in New Donk City are diverse
Breath of the Wild DLC, features more of the champions and amiibo, including Urbosa
Splatoon 2, male/female, selectable skin color playable characters, players in tournament were fairly diverse, 2 non-white male, 1 white female commentator
Arms, 4 female characters, 1 of color, players in tournament were quite diverse, 2 non-white male, 1 female commentator
Yoshi, Kirby, no human characters
Mario and Luigi Superstar Saga, human characters all white
Pokken Tournament DX, same commentators as Splatoon 2, diverse players
Xenoblade 2, no non-white characters shown, hard to tell if there was a diverse set of npcs in the town
Fire Emblem Warriors, only white characters shown
Sushi Strikers, some diversity in skin tone of enemy characters
Overall a fairly diverse presentation that highlights how Nintendo has made steps to invite a diverse set of players to their games, although there are clear ways that Nintendo can, and should, improve. Hopefully Nintendo will look at how well received Twintelle/Urbosa/Hau in Pokemon are and take steps to include more diverse characters like them in their games. I'd give it a 3.5/5 judging by how the Guardian did their score.