Interesting thoughts.
Personally, i think the Mad Titan does not really prove, that enemy is close...after all, the Titan you can produce yourself, are summoned from rest of the Dark Fleet as well, they are not newly constructed vessels like Titans of other factions. Obviously, since the Vasari are fragmented into many smaller entities, each with a possibilty to call upon their own titan, there are many more titans with the dark fleet out there. And it just happens, that a titan, whose crew went mad, is part of that fleet.
The only thing, which it may suggest IMHO, is that, there is not really any nemesis. Maybe its just whole Vasari race fallen into insanity, similarly to what happened in Event Horizon, or many other scifi movies/shows. Perhaps as a consequence of some failed experiment. And now they are running away basically not from another hostile race, nor from replicating nanobots eating up the universe, but basically from a threat, they will become insane themselves. Even though they are not aware of that.
In regard to blackholes, thats really interesting. Maybe its connected, maybe its not. Maybe the description is there just to "justify" the existence of these objects ingame, even though they would not make much sense otherwise.
Or perhaps the Arch-nemesis really is:
