I don’t think a wiki page can automatically evaluate the completeness of a route relation, even if it has been tagged with the total distance. I think it relies on someone editing the wiki to check with one of the relation analyser tools what the current length is and do the maths themselves before updating the page.

I suppose it might be somehow possible to write your own program that calculates the completeness and then somehow automatically edits the wiki page for you, but that sounds like a lot of work.

This page is just one of a number which is currently updated manually:
http://wiki.openstreetmap.org/wiki/WikiProject_United_Kingdom_National_Cycle_Network/National_Routes
so if you do come up with a solution it could perhaps be used on other pages too.