This diveunder has always been there, but in the past trains both to and from Ely had to share two platforms with northbound ECML trains. Now (in theory at least) there are two platforms for each of these flows.
In practice, most of the time ECML northbound services used 4 and XC, EMT and GA (the latter terminate!) used 5. Don't think I ever got an Ely line train in either drection that used 4 or an ECMl that used 5, though obviously the points allowed this. I'll bet that in practice that 5 now becomes little used- unless it becomes the default for terminating GA trains, with northwestbound XC/EMT on 7 and southeastbound on 6?