I am investigating using javax.sql.rowset.CachedRowSet in part of my application, however I can only find information on using the proprietary sun implementation com.sun.row
The question incorrectly states that the Oracle RowSet implementation is proprietary. It is not; it already is open-source.
The source code is released as free software under the GNU General Public Library (GPL) version 2 license with "Classpath" exception. Read the source code to see the license.
So they cannot be withdrawn. You and others are free to maintain or modify these classes provided you follow the terms of the GPL.
Also, some JDBC drivers provide an implementation of RowSet. I do not know if any are open-source, but that would be one avenue to explore.