In this morning's timetable updates came a load of changes for Good Friday (April 3rd), when Manchester Victoria seems to have lost most of its services. For example, stopping services from Liverpool via Chat Moss are diverted to terminate at Oxford Road.
This is pure guesswork on my part but I wonder if this is the first batch of timetable changes for a four-day blockade. Things will probably become clearer over the next few days.
Update 4 January: The remaining trains on Good Friday have been removed from the timetable, but at the time of writing Saturday and Monday still have normal service, and Sunday has lots of trains, with buses to Stalybridge. So either it's a one day closure, or there are a lot more timetable updates to come. Your guess is as good as mine.
Update 9 January: Saturday and Sunday and Monday have been updated, removing most trains, so it looks like the major disruption will be all weekend.
Update 13 January: A notice has now appeared on the National Rail web site, revealing that this will be a five day blockade running Friday 3 April until Tuesday 7 April. Not all the timetable alterations have been loaded in the database yet.