every couple of years I go back to check how's windowmaker/gnustep. Too bad the progress seems to have stalled and the support for some modern features is lacking, I would definitely be open to give it a go again
Note that Window Maker and GNUstep are two completely different projects with two completely different teams. It is just that using GNUstep with Window Maker gives a mostly consistent look (and feel, for the most part, though there are differences) if you use GNUstep's NeXT-like theme (GNUstep supports theming).