Regarding Site Content and Structure in SharePoint Online could anyone suggest an elegant solution, without a third-party vendor, for copying/moving subsites now that it is gone. I need to move a subsite from one site to another. You were able to do this through Site Settings > Site Content and Structure and I have not found any indication that this feature will return.
Not really an elegant solution, not my recommendation and probably not supported anymore but the page is still available if you know it's URL. You can get there by appending below URL to your site URL:
Alternatively, without making use of 3rd party solutions, you would end up using Microsoft's own SharePoint Migration Tool optionally combined with some custom development I guess.
I think it's safe to assume this Feature will not return. Given the fact that creating a flat hierarchy of Site Collections subscribed to Hub Sites is (justly) considered a better approach over creating sub sites.