I have a silly question, but why do we need MCConfiguration? Why not to have a package named SqueakPackages that will depends on all the package of the system.
Because you couldn't use that to interleave MC with other updates. What you're proposing is fine if you're only concerned in giving people access to the latest source code but it ain't working very well if you consider the kind of incremental updating process that we've usually provided. MCConfs give us the ability to go through the same steps again, if for example, someone wants to take a 3.8 image and upgrage it to a 3.9 image. If all that's involved is source-code changes that would work with a single "master package" as well but if there are intermediate stages, where certain versions of packages need to be present for the update to make sense you'll have a hard time to make that work.
Cheers, - Andreas