There are documents about the changes from previous versions.
Generally not a lot of things get unsupported in Base SAS. Other modules may have procedures replaced/consolidated/expanded or have some defaults change.
Strongly suggest before any migration that things that are stored in CATALOGS that you may use can be recreated with code or prepared for export so that they may be imported into a later version. Examples are Format catalogs. Without the code or data sets created with Proc Formats Cntlout option may be extremely difficult to recover across version boundaries.
Is your SAS server architecture and the OS it's running on changing? Are you changing user interfaces - SAS IDE, SAS Enterprise Guide, SAS Studio? Any changes here ae likely to have way more impact than any language feature changes.