Space elevators are limited in tension not buckling
Solid core things are not considerably stronger in buckling than hollow (there is some increase but not staggering huge like orders of magnitude)
Also with the exception of giant single crystals, the microstructure usually doesn't relate very closely to macrostructure. The best human scale I beam material does not resemble I beams at microscopic scale, for example the microstructure of steel is very important to its properties but has nothing to do with its behavior in an I beam. The best buckling material, if buckling even mattered which it doesn't, would probably not be microscopically tubular.
Space elevators are engineer-annoying in that it requires no basic research and not much engineering work to build a low-G one like on the moon, we have everything we need, yet one for the earth is at least one or two or three fundamental research steps away. Assuming you mean boring passive mostly inherently stable designs. If you want to make launch loops and rotor-vators then all bets are off and if you can handle the dynamic stability problems (and the massive cost) we can make those today. Note I'm talking about the engineering... we have industrial scale capacity to build a lunar elevator with materials that have been proven space rated, in comparison people insist on comparing them to earth elevator designs where at best we have theoretical calculations of theoretical compounds that might be almost good enough if they can be made at all, then made in massive industrial quantities and if they can be space rated. Spectra fishing line is good enough for a toy scale lunar space elevator, technically it would work but you'd get much higher payload with fancier stuff.
In my infinite spare time in my retirement or something I'm going to make a small scale launch loop capable of flinging snowballs or model airplanes or similar, or possibly never get around to doing it, or possibly end up a Darwin award winner. I can't even imagine what the FAA would think of a loop that I've calculated is technically within my ability to build and finance. Of course if the wire snapped I'd be in a substantial amount of trouble especially if it finally impacted a foreign country or something. In theory using relatively boring materials a large nation-state level effort could easily replace first and probably second rocket stages with a loop. One interesting solution to the reusable first stage problem is to not have one to begin with.
how big a loop do you think would be feasable to build, by a person such as yourself?
I assume you've looked at the equations (I have not), so how does a smaller loop affect the necessary speed of the rotor? does it increase or decrease?
Just spitballing, I'm no materials scientist, but the property of water which makes it so well suited to hydraulics is its lack of compressability. If these tubes can be crammed full of the stuff then it might increase rigidity to the point where it strengthens the tube's structural characteristics.
Even the name is cool: "water wires".
So beyond fiber optics we could have water wires? This should help photonics researches make a (faster) computer with light, right?