Well, PP why don't you share your point of view and knowledge with me and maybe I'll catch up somehow
Well, the OP mentioned extending the centreline from the Centre Fix. This means they already have the planned landing runway selected from the available approaches, including the approach itself (say ILS to that runway as an example). Therefore, doing what you suggest is just removing the approach and drawing a line from the runway.....which will be the same unless the approach is offset. All that will be missing will be CF and FF etc. Distance to go will still be the same. So I can't see any advantage in what you suggest, as the OP was talking about an approach that WAS in the FMC already, no mention was made by anyone to making an approach to a runway without an approach in the FMC or an ILS/DME for raw data? Maybe I am missing something?
PP