I have a theory about this (yeah, I know... "he has a theory, him and everyone else")... a common Hollow forms when a Plus/Whole degenerates into one because, for whatever reason, he has failed to pass on to Soul Society, or because it was consumed (or "converted") by another Hollow. Any Soul can become a Hollow - the mailman or your grandmother as much as the Desert Fox or the guy who shot down the Red Baron. A Hollow is a soul lacking it's "heart," or rather it's humanity, but it *does* retain, to some extent, it's memories and other characteristics of the person it once was. My "theory", then, is that most Hollows are as weak as they are because they are the corrupted souls of otherwise ordinary, common, or even "petty" people... whereas the Hollows that are capable of "ascending" out of the masses into an Adjuchas or even Vasto Lord are those that, in some way, were truly exceptional or powerfully important or even particularly heroic people... in other words, the Hollow formed out of a "great" soul is a "proto-Menos" (or perhaps a proto-Adjuchas or even proto-Vasto). Whatever Grimmjow was in life defined what he became in death - likewise with the other Espada... which brings us to Ichigo.
Ichigo is unquestionably heroic - his actions have directly and distinctly shaped the course of history both at home (by purifying Hollows that would have otherwise gone on to "truncate" the lives of other living people, including those who would later manifest their own powers and heroism) and in Soul Society (he was one of Aizen's key fall-guys for his conspiracy, then went on and helped to expose Aizen by thwarting Rukia's execution, thus winning the recognition and limited respect of Soul Society). The sustained presence of his spiritual energy in Karakura town alone has directly resulted in the advanced development of spiritual energies and powers in others. If he were to become a Hollow, and everything that I have presumed is true, it would be a prime candidate for eventually emerging as an Adjuchas. The really interesting variable here is that his soul did start "to Hollow" (<- verb) out, as we all know - but the process was thwarted, resulting in a soul that is both Whole and Hollow at the same time, in addition to still being alive and a Shinigami (a seeming paradox in and of itself)! There are some things we could probably say with some certainty about Hollows and Arrancar - but as has been mentioned, it would be a little narrow to talk about what is and isn't possible for Ichigo's Hollow, because Ichigo (and his Hollow) are effected by variables not present in any other character yet introduced (I mean the specific combination of variables - namely, being alive, a Shinigami, and a Hollow simultaneously - the Vizard are obviously both Shinigami and Hollows).
...All of that aside: one of the Vizard (Kensei?) distinctly recognized the attack as Cero. You would think he'd know, right?