The traditional authoring measure of productivity page count is meaningless in an on-line system, and grossly inflated in a system that uses two paper outputs from one data source. Traditional documentation tools are designed for adding content to format. To embrace the formatless world of SGML, documentation tools will likely change. There are several schools of thought on the design and implementation of SGML tools. Other organizations realize that authors who are creating data for multiple outputs should not see format as they are being exposed to only one representation of the data, not all of the mediums they are creating data for.
Authors are no longer in charge of creating a single deliverable.
Multiple deliverables can be created from the same data set. This raises many interesting questions including writing for on-line, information chunking, etc. Almost all SGML implementations start out as one or two deliverable products. Your impact statment should describe current method of operation and the effect of the new system on workflows. For example, camera ready copy will now be produced after authors are finished with content.