I recall reading somewhere that Kennington will become a Boundary Zone 1/2 (can’t find where now; the best I can turn up is an uncited claim on the List of stations in London fare zone 2 Wikipedia page.
A Nine Elms to Vauxhall OSI is admittedly very niche; the walk means that Oval (and stations further south) will be equal or better sticking with Vauxhall LU and changing at Stockwell, and London Bridge (and stations further north) will be better with other options via Waterloo. But as someone who lives between Kennington and E&C and has tried every way conceivable of accessing SWR services from home (none of them particularly seamless), it would be a welcome addition for me 🙂