Theory of Block Games says, the game is fundamentally a framework in which a number of systems interact. These systems are largely independent but can form a tiered hierarchy or tech tree.
But importantly, the best systems are those that repeatedly engage people in utilizing the core features of the game. Building, trading, and interacting with other people.
That is why everyone had a shop. There are hundreds to thousands of shops. That’s why everyone has a base, it’s required for progression. Within your base, you have some decorative or structural elements, but you also have your machines, and some storage, and these are all structures you have to build to do the game. That’s why Guilds are such a great improvement; lots of people had made guild halls before, but the new systems and things mean that there will be a lot more people getting together to make a proper “guild hall” to contain the helixes and such.
In Minecraft, especially modded, your base might expand to make a tower to put your Thaumcraft stuff in. Or you might make a little power plant that teleports lava in from a persistent block and powers things. Or you might make a little robot test room. Or you might make a factory that organizes and crafts items using pipes or something. Or you might make a nuclear plant, which needs to be separate from your base because it might blow up. These are all structures that implement the systems that are part of the game. Usually, a person is “done” after they have gone through all of the systems that they have an interest in and made their structure
And unfortunately, it’s why a lot of people make a base, then make a shop, and then do some hunts to power that shop, and check out. I think the reason that people say there is no new content, when there has been some decorative content, is because the number of systems hasn’t really changed, just the context in which those systems operate. Now, anyone can just go build anything, but ultimately… if it’s not a functional building, then you are building it for design or aesthetic purposes, which is fundamentally less rewarding than making something that people can interact with.
Now, Boundless isn’t Minecraft, but the fundamental rules of those systems stay the same. So the TL;DR for my answer is,
New content is anything that gives you a new thing to build. That’s basically the bottom line. You could say, hey, titans are not that, so what gives? And I will say, the main reason you would fight a titan, AFAIK, is to get the heart so you can build like a skyship or something. Everything comes back to building.
So I am super excited for Guilds, because as I said, it gives people new reasons to get together and build cool stuff. I am super excited for Farming, because people will start to build farm structures or greenhouses in their base (if that interests them). But similarly, ideas include
Land transit like trains. People are currently accessing everything via portals. But if you had trains, it would give you the chance to see things between points A and B, that you would not otherwise stop and look at. I think the snowball hunt was cool because it actually got people roaming on the planets where there were things to see, and people LOVE making long roads and infrastructure, so land transit would be something that gets people building AND gets them to see more of the nonfunctional things that have been built.
Titans, for obvious reasons, technology permitting
Stadium games. People are doing the best they can with bombs, spleef, etc. but simple logic elements in a machine that just, detects the presence of a person or a ball or something would give people the option of making more games to play.
Higher tier worlds requiring armor or other prestige equipment. Could be something like an “infuser” machine which takes lots of resources but allows you to access a higher tier or spark-rechargeable resource. I am thinking like, a hammer with a special ability that hits like a bomb used to and exposes materials, but can only be used a limited number of times before needing to be recharged by a spark infuser or something.
Renewable energy! Think windmills or solar panels that generate small amounts of spark per hour. Gives people a reason to build those structures if they want to for aesthetic or functional reasons. But this would make sense with more use of the spark mechanic.
And you get the idea. There are a lot of things you can do. I think you guys are on the right track. But the more people have things to build, functional buildings with high potential to interact with others, the better.