We definitely need OpenMQ, for want of a better name.
But what we also need are some other lower-level components to build these large scale systems on. And we don't really have these yet.
We definitely need a good, stable, scalable, easy to configure and manage RDBMS (NOT MySQL - that's a cardfile - PostGresQL? perhaps)
We need a development environment with REALLY good debugging support, including distributed debugging - and a good UI - there's nothing out there now. Plenty of powerful languages but all have very weak debugging support, particularly if you have client/server or n-tier components (i.e I want to put a breakpoint in a remote process and single-step it etc. as if I were locally connected to it). I don't care what language it is, Perl, Java, Python,C#,... just give me an enterprise-level development environment for it!.
Finally, we need to be able to use Mozilla as a reusable component. This is similar to how you would embed Internet Explorer as a COM control in, say, a VB program and have IE do all the user interface handling. Currently, because there's no inter-platform component service like COM in the open source arena, that's just not possible, even if the Mozilla control project wasn't so immature.
Alternatively, can we have Display PostScript like Apple and have a common rendering language for display and printing? with tools to support its creation.
Until we have these things its silly to wonder why large-scale Open Source projects don't exist. The plumbing is not there - apart from operating system low-level services the support stuff just doesn't exist.