In the future, we created a Dyson Swarm.
Each node (which I'd like to call a Gigalga) is an asteroid-sized, biotechnological, space-adapted, sentient plant that speaks the same evolved language as we do. The whole swarm can also work as a Skhadov thruster or a starlifter and/or as a hive intelligence that doubles as head of the system-wide government.
Apart from that, we also made artificial minds and tasked them to redesign entire planets, moons, and asteroids into gigantic, semi-sentient spherical, hard-shelled gas-bag creatures (called Astrophytes) that can choose when to generate gravity on their own surfaces. These Astrophytes can then grow to be more intelligent than baseline humans.
We basically transformed the solar system into an ecological paradise.
Every smaller creature, while not particularly as sapient as baseline humans, can now be made to understand our intentions. The same goes for the relationship between Astrophytes and baseline humans. In a way, everything can talk about everything else with every other thing, made possible by a nearly-telepathic way of communication that temporarily connects the conversing creatures' brains.
In short, aside from the sun itself, we chose to make every single thing within our system a living, breathing, understandable organism with a (more or less) semi-sentient life of its own that should be respected and lived accordingly.
In order to make that happen, the Gigalga swarm is constantly generating massive amounts of atmospheric molecules as a byproduct of their photosynthesis, which gets distributed evenly away from the sun and across the whole system.
Smaller creatures can even live on the surfaces of Astrophytes or within their innards. Zero-gravity adaptations can also allow entities to just float between these enormous Astorphytes since there's a system-wide breathable atmosphere.
Now, how plausible will such a world be?
Can this atmosphere be contained within the system by the Astrophytes?
Where might the reconstruction of spacerocks into astrophytes go wrong?
Are all the raw materials within our solar system enough to create that kind of atmosphere?