The plugin is mostly finished, but there are some issues on Word Online editor's side that we are working through with Microsoft. As this requires some back-and-forth and unclear when all issues can be cleared up we cannot give a release timeline.
Some of us are locked into MS word 365 by our institutions and need to be able to collaborate in the online, browser based version. I see Mendelay has an add-on for that, so can we please have a Zotero one? I know it's a non-profit fuelled by people volunteering their time, so this is just me asking nicely. I wish I had the skills to make the contribution myself.
Mendeley's Word plugin has thousands of negative reviews. Our goal is to create a version that actually works well.
(Also, Zotero is not primarily developed by volunteers.)