Do you think we can make wormholes?
Because if we can start thinking with portals to extend our range, we can do all that at once, through the use of multitasking and clones.
I have a theory. A flimsy one, and not entirely related to the question, but hear me out. I've been wanting to share it for a while.
It seems that magic is the universal force conducted by the soul of a human via feelings and emotions. In ordinary humans it's manifested as their "free will", i.e. an ability to choose their actions at any point in time. Granted, we don't exercise it much, from a certain point of view, but the potential is there.
In PMMM-verse, potential of a person is related to many factors: possibly strength of their emotions and convictions ( hope for the future), maybe the amount of suffering this person experienced and, almost undoubtedly, ties with other people.
It is, as I believe, the why of Madoka having such tremendous potential. You can also interpret the whole thing through the concept of karma, but I think that in the end it amounts to the same thing expressed in different terms. At least, I hope.
Examples?
Mami lucked out (?) by choosing a fortunate formulation of the Wish and generally dying at the moment she was making it, thus covering the first two requirements and maybe the third.
Homura finds herself in a similar situation, completing the first two requirements like a boss.
Kyouko rejects her Wish, thus renouncing her conviction, thus losing a part of her powers.
Sayaka admits "She was a fool" while falling completely in despair, probably admitting her intentions weren't thought out well enough. What with wanting a boy and becoming a champion of justice, yet not succeeding in either.
Ad nauseoum.
Anyway, Kyubei race found a way to refine this power and, so to speak, unlock the potential of a girl. I don't quite understand, but teenage girls were chosen as the target demographic, because they are more energy-efficient. I've read on TvTropes once that it's allegedly because teenage boys are more egotistical and self-centered. I'll get back to it. Anyway, girls are generally more emotive, and teenage girls are basically running all the time on high hormonal levels due to pubes- moving on.
The problem is, magic wasn't meant to be used that way. Generally, a person's life is spent trying to do stuff. Doing stuff requires two things: time and effort. They can be both managed to spend less of them, but not infinitely. When a Wish is Granted, causality and the universe in general is violated, because the girl didn't spend either time or effort to accomplish her goal. So the universe lashes back against the girl, the more grandiose the Wish, the more backlash. Oh, and if it was a goal of many more people than one who made the Wish, then the backlash is proportionally increased. Boys are egotistical, thus unlikely, to Wish for grandiose stuff, so the backlash is weaker, so the energy spent during Wishing and Witching out is less efficient. Or maybe they'd look ridiculous in frilly dresses, I dunno.
Anyway. Here is the answer for your question, Shadowhisker. Finally.
The Wish and intention helps shape the form the girl's magic. It can be used for literally anything, but because different girls have different goals, their magic adjusts accordingly. It is thus theoretically possible to do stuff other Megucas do, but very unlikely. Basically, magic is crystallized will and not very flexible. And well, violating physics evidently has its limits.
Disclaimer: I thought this whole thing up. I might be full of it. Firn may have different ideas than I do, not even speaking about Urobuchi, and I can't read minds.
And the system is completely broken by Sabrina and Madoka.
As a theory, Madokami has so much potential she basically suplexed the universe into doing what she wants, both in the canon and here, Sabrina acting as her direct agent in our case.
