All I know is that barriers are included (see Edinburgh City Council planning application 16/05341/PA). With the escalator being moved to run parallel to the main north-south footbridge/walkway, the ticket gateline will run from the end of the southern ramp to the lift, with the gap between the lift and the end of platform 6 being fenced off. Platforming arrangements aren't discussed but it would make sense to try to minimise the use of barriered platforms for the long distance services. In this case I think it's not the concept of barriers that's the problem but the fact that there would be so few of them, and so awkwardly placed, for a full trainload of passengers from platforms 6 and 7.
My understanding of it is that Platforms 5 and 6 are being extended eastwards. However, according to the plan of Waverley station on the National Rail website, there is no Platform 5 or 6 at present - I presume these are disused platforms that will be brought back into use, or renumbered from existing platforms?
It would appear that only Platforms 1, 2 and 10, plus 8 and 9 (the island platform outside the trainshed roof) and maybe east-facing terminal bays 3 and 4, will be the only remaining ungated platforms. Apart from 3 and 4, it would be difficult to gate those, although I suppose they could put gates at the bottom of the stairs and by the lifts on 8 and 9.
A lot of major stations were completely redesigned as open stations in the 1980s, and having to redesign them again as barriered stations must be a real headache, and probably none more so than Waverley, given its complex layout. In fact, I find it hard to imagine how Waverley must have been in the days before BR changed to open stations.