Anybody running without filters?
I think there is a lot of half truths being thrown around here.
Filters are useful for tanks without any means of nutrient removal, which are basically fish only tanks. It helps to break down ammonia to less harmful form (nitrate). I need to stress the word "helps" here, it is never a necessity. Nitrification can work pretty much anywhere, not just inside a filter. Tanks with means of nutrient export, namely planted tanks and some reef tanks, a mechanical filter is even less important.
A mechanical filter does not remove nitrogenous waste until you physically clean it, it merely breaks it down to less harmful form (nitrate) which will accumulate. Where as plants absorbs many forms of nitrogen compounds and remove them from the water. Altogether That is assuming the plants don't die and left to rot in the water. This is why it is possible to keep fish in a planted tank without water changes, without plants it is simply impossible. Therefore plant is a superior filtration to mechanical filter.
Fish poop on it's own is relatively harmless to fish. What is deadly to fishes is ammonia, which is constantly secreted by fishes through their gills. Fish poop and uneaten food is dangerous when they are decomposed by bacteria, which produces ammonia, which is deadly to fishes. Ammonia need to be dealt with as soon as they are available. They can be directly absorbed by plants.
As mentioned, nitrifying bacteria grows on all surface areas, and not just in a filter. A filter works by 2 ways. The first is to provide a growing surface for the bacteria. This is why filter mediums are porous objects, which has a high surface area to volume ratio. The second is the high water movement through the filter media heavily oxygenates these surfaces, a higher oxygen content can support a higher population of bacteria.
Both of those can be provided to a tank without actually employing an actual filter. The first though the use copious amount of substrate (which is typical in a planted tank), plant surfaces, or even porous rocks. In fact, unless you have a really huge filter, you are going to have a lot more surface area on your substrate than on your filter media. The second can be replicated through the use of powerheads (or even air stone), the higher the flow merrier, as long as your plants won't be uprooted by the flow and the fishes can take it.
Having a porous rock in a freshwater tank is different from the concept of using liverocks in saltwater tank. A liverock can have some denitrifying effect, deep inside it can form anaerobic regions that would house anaerobic denitrifying bacteria. This does not work in freshwater as freshwater carries a much higher oxygen content and anaerobic denitrifying bacteria can not achieve a meaningful population in a freshwater tank.
Also, apart from liverock, the popular methods for nutrient export in reef tank are algae scrubber and macro algae refugium. They work pretty much in a same way as using plant as a means of nutrient export in freshwater tanks. I personally keep reef tank with macro algae refugium for years without water change.