Based on previous project exp this is what I think.
1) SAP data archiving is more of a solution for ECC system . This helps you in finding which tables and so objects should be archived. It provided archiving tools of moving data from tables to flat files,
SAP than is able to retrieve data from those flat files automatically using same standard tcodes..
2) For BW data was moved to Informatica ILM , you can take a call to move historical data to that system to remove BW data load.