Hunch. Network Rail named 4 January on 14 October, as it named the day ahead of each of the five past closures, so nothing new sets this one apart yet.
The 4 January Paddington market resolves YES if from the start of service on Monday 4 January 2027 Great Western Railway trains run into and out of London Paddington to the planned timetable, as shown by Network Rail's completion statement and the National Rail Enquiries page for Dolphin Junction. A delay of hours caused by the works that morning is NO, a fault not caused by the works is not, and the Guardian and BBC News settle it if the official pages are silent.
We looked for cases where Network Rail closed a main London station or Birmingham New Street for holiday works that put in new equipment, and named a reopening day that was the first working day after the holiday. We found five such closures since 2007, all in London. Three reopened in full on the morning Network Rail had named.