The lack of extensibility in S1000D is cited as one of its main drawbacks and could be a deterrent to potential adopters. The main strength of the Darwin Information Typing Architecture (DITA) as compared to S1000D is its extensibility mechanism referred to as specialization.
One of the benefits of DITA specialization is that it not only allows users to extend the vocabulary to satisfy their unique needs, but it also enables the reuse of processing code (e.g. XSLT stylesheets) across specializations through a fall back mechanism to base types. The DITA specialization mechanism uses an elaborate scheme based on DTDs and XSLT 1.0.
S1000D should learn from DITA’s experience and success by providing an extensibility framework that allows any party to add extensions that are needed to satisfy their unique requirements. An S1000D extensibility framework will also reduce the number of Change Proposal Forms (CPFs) submitted to the TPSMG by allowing organizations and communities of interest to adopt S1000D without "polluting" the S1000D core specification.
The combination of XML Schema’s element substitution and type inheritance coupled with XSLT 2.0 schema-aware processing facility can provide a more robust extensibility mechanism for S1000D.
Efasoft has submitted a CPF (CPF_2007-006CA ) to the TPSMG to evaluate and implement such a framework.