Doctools and its formats are not big document processing systems, although they may come near with their ability to generate indices and tables of contents.
For example support for template text blocks and parameterization of such is limited to the very basics, i.e. the abilities to include a document into other documents and to set and get the value of document variables. There are neither conditionals nor looping constructs. Nor is it possible to define format specific text, i.e. it misses the ability to define different texts for web and print presentations.
The above, while possibly annoying in some situations, is not a very significant problem in my eyes. More serious to me is image support, or rather, the lack of it. While it is possible to use [uri] commands to insert a link to image into the text this will mean nothing to most output format, and in the case of HTML the result will be a regular a link to the image, and not an img tag. In other words the image will not be shown inline, but as clickable link to it.
There are some ideas floating around on how to remedy this, they will be discussed in chapter 7 about future work.