The DITA spec includes both <msgph> and <msgblock> elements for the content of software application messages, but two aspects of these elements' definitions seem to hark back to text-only interfaces and don't work well for modern GUI or web-based applications.
First, both elements preserve whitespace, with no option to treat whitespace normally. Modern UI messages typically don't care about whitespace, so it's restrictive and incorrect that this content model forces users to preserve whitespace.
Second, <msgblock> does not allow a <title>. Many modern messages include a title followed by descriptive text.
I would love the DITA-TC to consider these two issues for the next iteration of the spec. Both enhancements should easily be backward-compatible.