There's scant confirmed details unfortunately. However there was a consultation in 2022 for a very similar proposal which was rejected but is likely to be ressurected. The short summary would be making London Kings Cross - Edinburgh express services run fast between Edinburgh and Newcastle and between Newcastle and York, to cut 10 - 15 minutes from the end-to-end timing. This requires other services to have longer gaps between them so that they don't get in the way, and means there is likely to be a reduction in frequency or poorer spacing for other stations, especially for journeys like Northallerton - Newcastle, Alnmouth - Edinburgh, Berwick-upon-Tweed - London and so on and so forth. Some hours could see a third Newcastle - London service.