I'm a little rusty on my physics, but I do remember reading an article or a book on black holes. Aside from the creation of virtual particles at the boundary of the event horizon and a discussion on the evaporation of black holes, it discussed the matter of a black hole's density. One line that caught my eye said that, if an average black hole were expanded until it was as large as the universe, it would have a density equal to the current density of our universe.
Because it's almost 8 A.M. and I haven't slept in days I haven't taken time to read the full article. However, based on the two snippets I read above, I would have to assume that (if we're actually inside a black hole) our universe fits the de Sitter model. As far as the matter of a singularity goes...this is me whistling in the dark but follow along and see if it makes sense. Each galaxy has a super massive structure/cluster at its center which is the result of and the "glue" for the galaxy in question. Taking the principle of mediocrity (Put shortly--things are pretty much the same all over.) into account it follows that there is a very good chance there may be a similar structure/cluster (accordingly more massive) at the center of this universe. Perhaps (Come out on the limb with me!) the hypothetical massive structure at the center of the universe actually is a black hole singularity.
Anyway, just throwing stuff at the wall and seeing what sticks.