The calendar app has recently gained support for subscribing to third party webcal calendars (see owncloud/calendar#132). It would be great to expose these imported calendars via CalDAV (e.g. to mobile clients). Nextcloud would act as a kind of proxy service. One usecase is increased privacy for (mobile) users (only the Nextcloud server connection gets exposed to the original webcal provider).

Related nextcloud issue: nextcloud/server#1497