One app for all tenants: This will mean having a sole app with a “common” name for all the tenants and a login page without tenant styles or the tenant name.
Once the user logs in, they will see their tenant styles. There is some ongoing work to allow a tenant selector in the app main page, that will force the site administrator to make the list of tenants visible though.
Please note that mobile-specific site configurations will apply to all the tenants (like the Workplace distribution does). For example, if you disable an option via “Site administration > Mobile app > Mobile features”, it will be disabled in all the tenants. The same when adding new custom menu items, they will be displayed in all the tenants.