It sounds more like what is needed is common sense applicable in context, rather than the absolute right to break your journey on the cheapest ticket.
Common sense is that break of journey should never be prohibited if we are moving to an LNER style approach. There is no reason to ever prohibit people popping to the shops or for a smoke between booked trains (which is all BoJ is on an Advance ticket), it is just petty and makes the railway look extremely stupid. While relying on staff being sensible inevitably ends in tears, because a significant minority of staff have no common sense whatsoever.
There is absolutely nothing rational to say that if I have, on A-B-C, a through Advance, I shouldn't be able to pop out while changing at B, despite the fact that I could if I had separate A-B and B-C Advances which are probably cheaper anyway.
And if it turns out (rare) that a London to Edinburgh ticket is a bit cheaper than London-Newcastle and one person saves a couple of quid by doing that, who cares? Just bump the fares up a bit overall so your overall income is what you want it to be and stop worrying about it. It's easier to do that in a mostly Advances situation without anyone really noticing, another reason LNER likes the scheme. The main situation where you'd get an Advance being way cheaper than a shorter journey was inter-TOC competition at specific stations, and now DfT gets all the revenue (OAOs aside*) there is no need for this to persist in any form.
The railway is almost surpassing Ryanair in the ability to be utterly, utterly petty, and needs to pack it in as it benefits nobody.
* Another reason not to have OAOs, then....
