years of experience with lunkheaded metal kids who want to tune their guitars lower and lower, and think that just putting on bigger and bigger strings will get them there.
past a certain point the note is just too low for the scale length, and no matter how big a string they try to put on there, it still sounds weak, twangy, and unfocused compared to an actual bass playing the same note. you get less and less fundamental, and more and more harmonics the lower you go.
in fact, past a certain point bigger strings make it worse, as the string just gets too stiff for its length (due to being so thick), and the harmonics just get even further out of tune with the (barely audible) fundamental.
translating this principle to basses, we all know how it's not easy to get a low B to sound as good as the other strings on 34" basses. it's easier on extra-long scale basses, but even so, builders have to really focus on getting that B to behave, as it's really "too low" of a pitch for a bass guitar. once you go another string down from that, all bets are off.
i've played not many, but a few nice 7-strings from the likes of roscoe, and even at 35", the F# is just a novelty noisemaker.
my real point is just that people seem to think you can put bigger and bigger strings on a given instrument and tune it lower and lower ad infinitum, when in fact once you get out of the natural range of the instrument, you get diminishing returns in the form of less and less fundamental and more and more bad harmonics.