Interesting concept, but ditching some chemicals is a pretty spicy stance with the relative non-impact on fish from dechlorinators. Some notes and questions:
Why not use dechlorinator? Even low chlorine concentrations of 0.3ppm can be fatal, especially at pH levels between 6 & 7 (
source). Tapwater can have up to 4ppm of chlorine in (
source) so even a 25% waterchange can have up to 1ppm chlorine, and it takes only 1.2ppm tap chlorine to reach the fatal levels once diluted. Not all fish are as susceptible but the point stands. Small waterchanges often fail to remove excess nitrates and organic molecules such as hormones. As you mentioned free chlorine may be lower, but it's not a risk we really want to take.
Chloramine is far more stable and unlikely to gas out of the water compared to chlorine. I don't see the issue with using a dechlorinator, can be made super cheaply yourself.
Diseases still happen at a far greater rate in aquariums than in wild fish, or at least more intensely. Preemptive use is discouraged by most people, but what do you do when a disease takes hold?
You want to maintain a huge plant mass without co2 or ferts? How do you intend on doing that? Plants need a balance of their nutrient and carbon uptake for proper, healthy growth.
pH is always so fussed over, the best thing is stability. Consistent, large water changes keep the buffering capacity of the aquarium up. Provided you keep the temperatures similar it is generally the preferred method as it removes large amounts of material that can't be filtered out like nitrates, hormones, and other organics. With proper filtration ammonia spikes can be avoided.
I am poking lots of holes into this as I am interested in the discussion.