We should be encouraging users to use the catalog views. Many hold on to INFORMATION_SCHEMA for portability or standards reasons, but they may not be aware that the views have not been updated for new features (a couple of examples off the top of my head: filtered indexes and included columns).
The main documentation page for the I_S views contains a couple of warnings:
Some changes have been made to the information schema views that break backward compatibility. These changes are described in the topics for the specific views.
Information schema views provide an internal, system table-independent view of the SQL Server metadata. Information schema views enable applications to work correctly although significant changes have been made to the underlying system tables. The information schema views included in SQL Server comply with the ISO standard definition for the INFORMATION_SCHEMA.
While these are an indirect admission that the views are not complete, I suggest a more direct confirmation. At the very least, the second note should be expanded to explicitly state that the views have not been, and may continue to not be, updated for all new features. The note should also be included on all INFORMATION_SCHEMA view topics.