I would also be rather conservative with regard to adding packages that are not developer tools.
If we add XML we should probably also add XYZ. Wouldn't it make sense to add Seaside too? The problem here is not primarily the larger image file size, but the image becomes bloated in general (e.g., search results) and there's a risk of conflicts (e.g., we are using the pharo-dev image, but with our own Seaisde 2.9 version; if the image comes with a preinstalled Seaside 3, we couldn't use it anymore).
It appears to me that preloading packages like XML is just points out that a good package manager is missing.
Yes for example moose people get problem because when they load the latest version of XMLsupport on pharodev1.2 the system barks. While pharo-dev (with tools not frameworks) is an ok image to build systems like moose. Stef