<apologies, I'm not able to @ mention folks who asked questions above - hopefully you all see my replies!>
Benoit - No, I'm sorry the mailbox language won't follow the designated default site language setting, but that's great feedback! Same with the setting of different managed paths by template; a request we've heard and are evaluating, but it isn't available with this update.
Tony - the admin creation experience will, but self-service site creation will only provide the user with one or the other (depending on their permissions).
Kelly - if you'd previously selected "hide the subsite creation command" we continue to honor that with the update, but it now applies to all modern sites.
Luke - sorry for any confusion. We are still firmly committed to moving toward a hub-site world; the updates to subsites are strictly around creation settings - to actually to make it easier for admins to hide for *all* site templates, while still providing an option for those not ready to move fully to a hub site architecture. Same with offering the non-Group connected team site; it's to provide a modern option in self-service site creation for those customers who aren't ready to enable group creation.
Srikanth - we'll be implementing hidden as the default, but this would only affect new tenants; we aren't changing your current settings (just expanding what they do).
Barbara - for (1) - this is an option we're currently evaluating (but note that it would only be available to site collections, not subsites). For (2) - yes, these changes only apply to self-service site creation. SharePoint admins will still be able to create sites from tenant administration.
Denis - No, the self-service site creation ux will only provide the team option your eligible (group-connected or not); there won't be a choice. SharePoint admins will be able to choose which template through that experience.