What are the latest developments about global stilling?
It seems to be a thing of the past. Apparently around 2010 the 30 years calming trend reversed. Since then, wind speeds and wave heights are picking up quickly, possibly in a decadal variation pattern.
Young et. al. 2010 Global Trends in Wind Speed and Wave Height
Possible application for the planning of wind turbines:
Zhenzhong Zeng et.al. 2019 A reversal in global terrestrial stilling and its implications for wind energy production
From the abstract of the latter:

... we use wind data from in situ stations worldwide to show that the stilling reversed around 2010 and that global wind speeds over land have recovered. We illustrate that decadal-scale variations of near-surface wind are probably determined by internal decadal ocean–atmosphere oscillations, rather than by vegetation growth and/or urbanization as hypothesized previously. ...

Similar observations of an increasing trend over ocean surfaces, overlapping with the period of global stilling over land.
Ching Wei Zheng et.al. 2016 Global oceanic wind speed trends
Can only read the abstract of the latter. Would be interesting to investigate further the reason for the differing observation and modelling of sea- and land-wind speeds during the term.