Oracle and MSSQL have a REPLACE function (see http://docs.oracle.com/cd/B19306_01/server.102/b14200/functions134.htm). It is not in the SQL standard, and in fact the standard has no equivalent function.
REPLACE is not a reserved word. Therefore the implementation will need to add REPLACE to CommonNonReservedKeyWord() in the parser.
Note that Drill and potentially other users of Optiq use REPLACE as part of CREATE OR REPLACE syntax. Careful not to break that.