There's another likely reason to move platforms along the line - to steal the old platfoms for something else. The obvious something is a metro, and we've seen that at Twyford and Maidenhead, at least operationally. In both cases the service now has a dedicated bay, and being a true (one-ended) branch there has to be linking track. Slough was already like that.
Are there any cases that go further? Where a side-route service now has to terminate at a platform further along its line, instead of running into the station? Replacing trains by trams (as at Wimbledon) shouldn't count.
I can't think of one, except by going further abroad and re-citing the re-siting of the Saint-Lazare platforms at Ermont-Eaubonne. This was an odd station all along, with extra lines joining the main through ones at both ends. French Wikipedia has before and after diagrams, which helps:
The Paris-Nord lines divide and there's a track pair and two platforms for each west-bound line. Both are suburban, though the Pointoise line is still called "Dieppe" despite being cut short at Serqueux ages ago. The southern line to the east, now the RER C, is the bit that branches off by the Eiffel Tower and crosses the Seine on a curved bridge, before trundling through the basements of north-west Paris. It also has a link into Paris-Nord, which was used by a circular service pre-RER. The southern line to the west goes to St-Lazare, and its service terminated here and could not get onto the main line anyway. The RER also served a bit of this line before disconnection.
Having decided that the RER and Paris-Nord suburban service to Pontoise needed more than their two platforms, some quite serious engineering was applied to transferring the third pair to the RER and building new platforms on the road bridge and embankment instead (about 200M€, including the station itself).
Now, is there anything like that round here?
