The current version of the Workbench / Documentation Tools still produces the style used in Mathematica 11.0 and earlier.
This style can also be displayed (mostly fine) in Mathematica 11.1 and later. The few problems (such as large font in See Also links) can be corrected by post-processing the generated documentation notebooks (this is what I do for MaTeX). You don't get the latest look, but you can get working documentation that is compatible with many M versions and still looks good.
However, the reverse is not true. At one point Wolfram accidentally pushed a Workbench update, which produced documentation that was not compatible with earlier versions. You can imagine that this is a big problem for anyone who develops Mathematica packages. WRI only needs their documentation generator to work with the latest Mathematica. But any useful package will need to be compatible with some earlier versions too (my impression is that at this point most, or at least a signification portion of, M users don't use the latest version).
Thus I very much hope that when Wolfram releases an update to the Workbench, it will still be capable of producing backwards compatible documentation (or at least make older Workbench versions available).