Does the possibility of a hypertextual philosophy call into question this time-honored assumption [of a subject in total control] in the philosophical tradition?

This question doesn't seem clear: if philosophy is in the old self-possessed style, then doing it in hypertext does not of itself call the assumption into question. If it is in a new style then philosophy has already called the assumption into question, and hypertext is not the crucial factor, though it may amplify the effect.

It's clear that hypertext can't be a necessary condition of questioning the assumption (of possession of the work), since that assumption has already been questioned in the linear texts that the questioners are appealing to. It's also clear from the questioners' very questioning of Socrates that neither is hypertext a sufficient condition of such questioning. (Unless they think that Socrates isn't really hypertext, but that's a dubious essentialism.) So it seems that the possibility of a hypertextual philosophy does not by itself call into question the time-honored assumption.