Track changes seems to be high priority. We used to have it, but decided to remove it until we achieved stability. In the meantime we exchanged a lot of the foundation of Fidus Writer, so we have to program a lot of that again, but the design for the user interface elements is there.
juca So far most users have just used the provided ODT/DOCX templates, but it should not be that difficult to add some error tolerance for user created templates as well as documentation.
Latex templating is more difficult as Latex files don't separate formatting from content in the same way. And for feature, such as bibliographies or tables, there are several competing packages that each work slightly different and that cannot always be used in all combinations. Basically, we just chose one relatively up-to-date package for each of these that seem to work together in most situations, added some glue to have those packages work together, and then sue that mix for all output. Should the user want to choose another package, for example to handle tables, this may also influence all other packages used for other features as well as the glue code.
So for Latex I cannot see how we could make a simple templating engine. But what we could do would be to put the latex exporter in its own plugin and then let people with programming skills fork it and create their own versions that use other package combinations. @juca would that be of interest to you?