Regarding the case of a feature being added in Moodle 1.6 and then modified in 1.8, I think what we should do depends upon how the feature was modified. If bugs were fixed, or small improvements were made, then a 1.8 template is not necessary. If a new feature or sub-feature is added, then a 1.8 template may be used.
Rather than adding lots of version templates to a page, you can always type "From Moodle 1.7 onwards, ..." or similar (for example, in the My Moodle documentation).
Ensuring that Moodle 1.8 is fully documented is an excellent plan. Please keep up the good work!
