[lmm]

>Essentially, I envision a build tool that takes in a huge number of arguments (maybe reads them from an XML/JSON/whatever config file) with sane sets of defaults for each.

That's pretty much how maven works. A typical java project will have an xml file listing its name and version, the names and versions of all its dependencies, a scm URL for tagging releases and that's basically it. The problem is people who have got used to having all the freedom of calling arbitrary shell programs at any point in the build process; it's very easy to accrete a series of small hacks ("oh I'll just sed this file here to fix that") that add up to something incomprehensible.