My question here, is that just because the MaBiT explains the mechanics of the situation, it doesn't truly answer the question of why we never heard of this class of punishment until now, something I believe the MaBiT himself acknowledges in recognizing his isn't a complete answer to the original question.
There's actually another question of interest that I came across this Shabbath: Reb Natan in Likkutei Moharan I:112, brings down Masechet Menahoth 29b in which it is explained that a person cannot return through the same opening which he strayed, rather they must open for him a new opening. If this is the case, then the MaBiT's metaphor for Teshuvah seems to contradict our gemara here in Menahoth?
Since this whole post is sort of a side note, I'm compelled to take you on two more related tangents: In discussion of this idea, that someone cannot return through the portal through which they fell, Rebbe Nachman answers Reb Natan's question explaining something unbelievable: When one falls, one can ascend through an opening through which someone else, your friend, fell, because when someone (named A) falls from on high, he is still higher up than someone else. (named B) In this manner B can actually rise through the portal through which A fell. Meaning that when a person falls it is sometimes for the purpose of the aliyah (yeridah l'tzorech aliyah) of someone else.
The final step in this winding post is the Noam Elimelech's explanation in the end of parashath Naso, in which he explains what it means that someone could perform a sin for the sake of heaven: Sometimes a Tzaddik needs to perform what in his eyes would be a grave sin, so that he can reach down to such a level that he can have a connection with even the lowest of people such that he can bring them blessing and shefa. This, he explains, was the problem with Shaul HaMelech who was without sin, he couldn't relate to and bring blessing to the lowest of Bnei Yisrael, even though it is the King's duty to do just that, bring blessing to all of Bnei Yisrael.
To tie everything back to the previous post I must share two more points: Rebbe Nachman explains (in Likkutei Moharan I:112 mentioned above) that the only way to illuminate the darkness when you have fallen is through speaking words of Truth. Truth being the light of HaShem, nothing can hide from Truth, so even the lowest and darkest places are illuminated in the presence of spoken Truth.
Why spoken Truth? This plays off of the Pri Ha'aretz on parashath VaEra, the weekly parshah just passed. Rebbe Menachem Mendel of Vitebsk, the Pri Ha'aretz, reveals that when someone knows and recognizes that all his speech is not really his own but rather emanates from HaShem Himself, then through his speech he can create worlds, just as HaShem's speech did in the creation of the world. From this we can see, taken together with Rebbe Nachman, that when we speak Truth from the deepest places, it becomes clear that we are not speaking at all but instead it is only HaShem who speaks. (Perhaps this is one of the deep secrets of Mechayey HaMeitim, as we know that the Targum of a "living soul" is a "speaking spirit," and a sinner is considered to be dead in his lifetime.)