Snom does support LDAP directory lookup for ages. It also supports vCard import.
However, it seems that CardDAV  is becoming increasingly common, particularly in small to medium-sized enterprises .
Therefore I propose adding native CardDAV support to Snom phones in order to lookup contacts stored on CardDAV-based servers. Part of the required code should already be available with the existing support of vCard (data storage format) and LDAP (lookup mechanism) and may be (re)used.
 Many groupware solutions targeted at this kind of customers (take ownCloud/NextCloud/*Cloud as an example) support CardDAV instead of LDAP. These groupware solutions become increasingly popular as they facilitate syncing with mobile devices, where the CalDAV and CardDAV protocol family excels. It is only natural that these kind of customers wish to sync their business telephones with the same dataset as they sync their mobile phones with.
Thank you for the suggestion and details. We have an open feature request for this in our system, with ID SCPP-3560. We don't have an estimation for the implementation yet.