But there is, in a way. Arts, they manipulate the ether and depending on the user, can raise their ether control and concentration. If Aionios soldiers are ether reserves, it makes sense to have them concentrate it in their bodies. It keeps the reserve active and constant for when it is needed to supply the Trinity Processor and maintain the world.
The war also prevents other certain... imbalances, like reproduction. If the people of Aionios were to reproduce, it would break the balance of the system established by The Consul and the Queens. We already saw how that went with Lord Zanza and how the Telethia were needed to resolve "the problem".
Though maybe it can also be looked more like a manipulation to keep the world stable without the Conduit. It wouldn't be that improbable in a combined world. You can create life with core crystal and any remain of The Architect's nanoparticles. A process you can control via mastery of ether, the principle of life. You only need people who have mastered ether to assist, and that's where Melia and Nia come in.
Well, if the virtual world theory holds true, ether is just virtual like everything else.
If it's taking place in the real world, I can't think of a way to make ether rare or commodified.
I don't know what's happened between the end of xb1 and xb2 and xb3..... But 'ether' was so saturated in both universes, making it scarce enough to need to stockpile reserves sounds like something really hard to do. It was so prevalent that not only did it saturate all matter and living beings and plants, but the excess made massive nano machine oceans gigantic titans could swim around in, swallow big gulps of, and process into a super dense state in mass quantities.
Ether is nanomachines, the output mechanism of Klaus's reality machine. When the reality machine and its safeguard/command interpreter trinity processor is online, ie when there is a power source capable of powering it, it can use them for data sensory intake on a planetary scale, run highly accurate simulations on what's going to happen based off of that data (visions), break down matter for raw atomic materials, disseminate/absorb/redistribute/transform energy, and reassemble atoms and distribute said energy to construct new creations like a fancy 3d god printer. Up to creating a new universes big bang, it can control matter and energy with such precision, that if desired, somebody could literally write a script that plays out for thousands of years controlling every living being on the planet like a scripted puppet, with very little precision errors accruing over time (but errors accrue over time nonetheless, as Alvis explained after the party was retreating when Zanza revealed himself, even without Shulk, errors inevitably accrue over time until they become too big to be resolvable and crash the pre established harmony of events prompting Zanza to perform the the ritual of death and rebirth). Introducing a second scripter that you can't directly control could have catastrophic consequences for the script much much sooner though.....
When it is offline, or you don't have access/authorization to the reality machine, they still saturate the environment and flora and fauna, but are just inert, they can be activated on a localized level by technology like the replica monados, more primitive technology like ether rifles, and ether cylinder based tech, and innate abilities (originally programmed into created beings via the reality machine way back when) like high entia ether manipulation, and agnus ether manipulation.
Without the conduit, or a power source of a comparable magnitude, ether can only be activated on a local scale.
Unless xb3 flips the script, the availability of ether likely isn't the trick, it's saturating everything. It's the power needed to activate it on a massive scale, and process all the data it can gather that's the macguffin.
