Uru is a mix-mash of many concepts. Having multiple activities besides exploring and puzzle solving feels like it would fit.
Personally I think it's a great idea since it means every activity is optional and you and your friends can switch whenever you feel bored, since each activity is its own Age. That's something that became popular more recently in games like Fortnite, Minecraft servers, or more recently Core games. With the exception that Uru's lore still ties it all up together, so you can go chill in Kahlo to discuss the latest tournament, or check who is the highest pellet-dropper. Immersion is important to Myst fans.
In contrast, leveling in other MMOs is only there to keep content away from you. What little minigames they have is (in my experience) trash and not really tied to the story, so most of the time spent is on boring grind.
The problem, as we've said with Aloys, is that this vision of Uru means a huge amount of developer work, and thus a high cost. Every new Age means redoing from scratch the gameplay programming and environment building. Few companies can do it, and even then you have to cut some corners.
(How many different activities were supposed to make it into Uru ? Let's see... Exploring, puzzle solving, socializing, climbing, discovering D'ni's past, playing marker quests, dropping pellets, looking at the wildlife from the Pods, playing games in Jalak, driving vehicles, racing in Kahlo, hunting people in Rebek, gathering materials in Dahtamnay, climbing the Gahreesen Wall, playing Ayhoheek, raising Lakis, hunting in Pirahnay, shooting lasers in Jellyfish, battling on chicken-back in Pento, and I probably forgot more of those. That's plenty. And that's without counting the out-of-the-game activities.)