Matter and energy exist, though there are different forms of each.
For matter, this is simple. Obviously you have different states of matter, different elements, but if you break it all down at the end of the day it's just stuff, whether you want to talk about atoms or baryons or quarks. There is of course the interesting quantum question, of whether these end up just being waves if you look at them closely, but given that waves are typically free to dissipate there is plainly something non-wavelike about matter. All of which is a drastic oversimplification of quantum theory, but it merited acknowledgement.
At a basic level we can break all matter down into this stuff. There are interactions with energy that help distinguish it all, but this provides a simple visualisation. On a macro scale it is even easier to see; you can have a solid cube that you drop into water, say, and it cannot occupy the same location as the water. However if the cube is porous, you end up finding that the water and cube essentially may indeed occupy the same location, the water running through the cube, or the cube running through the water, whichever way you want to visualize it.
Energy, now, is where it gets interesting. There are many types of energy. Heat energy, which manifests essentially as the vibration of molecules (also as a form of radiation, that is waves). Sound energy, which really is just an illusion born of human perception, it is again just vibrations that go through matter, but when those vibrations reach our eardrums it is interpreted a specific way by the brain. Again, just vibration. Kinetic energy, obviously, is just the movement of matter. Electrical energy is manifested by the movement of specific types of matter, and this is when we get onto concepts such as chemical energy, potential energy stored that one day could manifest as another type of energy. At a basic level energy and movement are equivalent.
And then we get to light. Though it is modelled as a wave, and it can indeed impart other forms of energy, it does not seem to be as simple as a vibration carried by matter. The trivial resolution to this is the photon, positing that the photon is the particle which carries the wave of light and thus vibrates in such a fashion, but this is unsatisfactory. It does not allow for wavelike behaviour. What does, however, is ironically simple: multiple particles.
Think now of the famous double slit experiment, only instead of photons, we use water. Water waves interfere with each other, create similar patterns to light, but if you then constrain what happens to a single molecule of water going through at a time, you no longer observe the interference pattern. Understanding the double slit experiment, really, is trivially simple. If you limit things so that you can observe a single basic particle, it no longer has anything to interfere with. Only when things are unlimited, when there is no equipment getting in the way to allow you to observe, can the interference occur.
Light, then, is similar. The notion of an 'aether' that carries light must indeed be accurate, it just wasn't as it used to be posited. The light waves themselves are carried by multiple fundamental particles, photons, that only behave the way they do when they are carrying lightwaves. One might say they are synonymous with light, but at the end of the day the two statements are equivalent; energy cannot be created or destroyed, the emission of a photon simply creates the photon by converting it from some other non-photon potential. Something is done that transforms it into a photon, the addition of 'light' if you will. It then carries this light, and we observe all we do.
The only thing special about light, in this case, is its speed limit. As I hope we all know, anything with mass that approaches the speed of light in vacuum ends up warping spacetime around itself.
So far I'm just expressing what is already known, albeit with a couple of odd bits of focus.
My proposal is thus: there are two building blocks to everything. Movement, and stuff. Movement gives us energy, this 'stuff' gives us matter, though precisely what type of matter depends on energy. There is no more and no less than this. Light is a massless particle with a 'charge' of energy, creating a photon.
This is in line with all we know. The extension is where this gets interesting.
I glossed over photons just now. They are converted from a potential, yes, but what is this? Are lightbulbs haemorrhaging matter without losing mass? We're treading on the toes of thermodynamics with that thought experiment, but it is an illustration. Perhaps it is raw energy converted into matter, we know this is possible, living things do it all the time. The quantum understanding of matter makes this easy; what sets apart a wave of energy and a quantum wave of a fundamental particle of matter is perhaps most simply thought of as some kind of binding that keeps it in place on a macro scale. So long as that can be generated, energy becomes matter.
The third option, though, is the aether response. Instead of a medium which carries a wave, it is a medium composed of stuff already, and the introduction of a light-charge simply shifts a particle of this into a photon, in the same way a colour-charge defines a quark. If there is such a medium it must be universal. If you want to imagine it as a sea of molecules, a light-charge essentially transforms one molecule of substance A into substance B with wholly different properties, such as a velocity.
And thus, we reach the conclusion of this. I propose that the medium of light is spacetime itself, that spacetime is composed of another fundamental form of matter. This isn't an alien idea, John Wheeler hypothesised a type of quantum foam, this is simply a generalisation of that.
Location, then, is much like the porous cube mentioned above. You occupy the same space as this primarily non-interacting matter. In a similar fashion, this also means that the speed of light in vacuum is not a property of light, but rather it is the limit to the movement of the fundamental components of spacetime. If a mass is moving at high speeds, it moves faster than the space it occupies can keep up with, of course that is impossible. Relativity begins to make intuitive sense.
I could take this to more speculative ground, analyze why the postulates of relativity are what they are, rather than merely stating it. One could suppose that the particles composing spacetime are locally uniform, thus any force that keeps them together, limiting movement and causing the speed limit, will be constant. In this way, the assumption of the homogeneity of spacetime and the speed of light in vacuum being constant are equivalent. It also tells us the situations in which relativity will break down, and why, taking us a step closed to a unified model.
This is just a lot of theoretical underpinning to the concept of spacetime possessing some form of building block, and by extension the potential for varying concentrations, but I hope it begins to demonstrate the ramifications for even understood science. A lot of topics are treated as big mysteries, or "This is just the way it is," but there are answers to the why as well.