You could argue that a split that's only available for Advance tickets and only with the same TOC isn't really a split in the conventional sense at all. All that's really happening is the pricing model behind the Advance ticket tiers is gaining increased granularity for where a cheaper tier is available in part but not all of the customer's journey on that train.
It never made any sense in the first place for an Advance to be available only at the lowest tier that was available for the customer's entire journey on one train. It stymied operators enormously by making tickets for long journeys very very expensive if the quota was sold out on a short 20 minute segment, or blocked the sale of an Advance entirely on a train which had large numbers of empty seats for a high proportion of its journey, but no quota remaining for a short segment, causing them to remain unsold when only a very high Anytime Single price was offered. It only got done that way because of the product types inherited from BR (who even used to require outward and return quota to be available on Advance Purchase Excursion products).
To continue with my example of the 1730 from London to Edinburgh, LNER will be able to offer one ticket at the rate of almost the Anytime Single price from London to Peterborough plus a much lower Advance from Peterborough to Edinburgh, thus better matching supply with demand.
Of course, if LNER are permitted to keep mandatory reservation long-term, they will likely try to use this to deny boarding of large numbers of low-yield season ticket holders. Alternatively they might be permitted not to accept Seasons at all in future. You can be certain that, however it's achieved, LNER will want to offer first refusal to high-yield customers.
I suppose if there was disruption, you'd still need to know as you'd need to take alternative trains that stopped at the split points.
Has it been confirmed that a ticket once issued actually tells the customer what the split points are?