Swift Playgrounds: Replacement for captureValue(_:withIdentifier:)
There is currently no alternative or replacement. Graphs are only displayed implicitly. I have verified this in the Swift/Xcode labs at WWDC 2016. I have filed a radar and will update this questions, should there be any progress.
Use the currentPage
property:
XCPlaygroundPage.currentPage.captureValue(_, withIdentifier:)