Blog Post
Do you really expect to be able to replace COM/VSTO addins with the joke that is OfficeJS? It doesn't support the most basic of things like drag and drop. Many Outlook addins have deep system-level integration, which will be impossible to replicate with OfficeJS.
I understand the reasoning for wanting a cross-platform addin architecture. But it needs to match what you can do today with VSTO. Also, .NET is cross-platform today, why not use that.
Also, you link to the suggestions forum for OfficeJS. That place is a joke. There has been no response to multiple requests for adding drag and drop support: https://techcommunity.microsoft.com/t5/microsoft-365-developer-platform/support-drag-and-drop-to-from-officejs-addins/idi-p/3017629, https://techcommunity.microsoft.com/t5/microsoft-365-developer-platform/drag-and-drop/idi-p/2377183