As the current Release Manager of ImpressCMS, I am quite aware of the weaknesses we need to look at in following releases.
One of the major weaknesses that makes ImpressCMS a difficult sell is the fact that you need to use an FTP client in order to add modules or themes to the system. Most systems have a capability of installing those elements directly from the administration interface.
MrTheme just demonstrated the power of open source. While ImpressCMS is in feature freeze during its 1.3 release, he had an itch that needed scratching, so he developed his own solution for it.
Granted it ‘only’ installs the latest stable (ImpressCMS 1.2.4) or the latest beta version (ImpressCMS 1.3 beta – just released), but it can be used to upgrade your sites without hassle. For me, that’s one first step towards an online updater, but now I hope the community will step in and help MrTheme out.