The amount of mathematics knowledge present on this website (in the form of questions, answers, comments, and people) is now truly enormous. I think that exactly one year ago almost all possible questions involving "basic mathematics" had been asked and answered along with a substantial number of questions involving "intermediate mathematics" and some questions involving "advanced mathematics". Of course, in this classification I am specifying an equivalence relation defining precisely when two mathematics questions are "the same"; my definition is that "(question A) $\equiv$ (question B)" if and only if the underlying sets of concepts and ideas (in a broad sense) used in the definition and the solution of each of these questions are "the same" (in a broad sense). In this case, the number of questions involving advanced mathematics is still infinite but we can reasonably state that the number of questions involving basic or intermediate mathematics is finite (provided that we suitably define "basic" and "intermediate").
However, now it is difficult to find a concept in mathematics about which has not been asked on this website (including very advanced and esoteric concepts). In fact, many of these questions have also been answered indicating the amazing breadth and depth of knowledge possessed by the community at the moment.
It would be great to have a few more specialists in some of the more esoteric topics in mathematics actively participating on this website but at the moment there are at least a few specialists in each of the "major branches of mathematics"; I think that in exactly a year of time the community will be extremely vast in terms of mathematical interests and knowledge. I think at some point in the future (I predict almost definitely by 2020) we can expect this website to be not only an extensive and deep library of mathematics questions and answers but also a place where you can reasonably expect to have virtually any mathematics question (of bounded difficulty where the bound is a nondecreasing function of time) to be answered very quickly (of course, this will have advantages and disadvantages but I think that the advantages outweigh the disadvantages).