@Doitsu, @DiapDealer -- I can tell that PageEdit is not directly integrated with Sigil as of now (and I have built it from a git checkout and played around with using it), so it would seem more like multiple independent tools that *happen* to be things where people who use one probably want the other as well -- but the same thing might be said of Sigil and calibre.
Principally what I was wondering was whether any closer integration was planned. For example, an analogy could be brought to the FlightCrew plugin (which bundles a heavy binary in the distributable, rather than attempting to find one on the system before e.g. downloading it from github and checking the hash).
If not, then I guess my current plan is just to package it up as "another useful application". I could be convinced to add it as an optdepends of Sigil...