Ingest is one of the most time consuming operations when using both backup copy and multiple cards/readers so I like the way you may set multiple sources to be ingested and after setting things up you may leave PM and do other stuff even go get some sleep....if no deadline rush.
For such instances and cases when I have shot more than one assignment on one card it would be great to be able to set up more than one different ingest. Not only differing in sources but having different target paths directories, even different IPTC stationeries. I don't know if it is possible or not, but since PM does ingest in the background maybe it could be somehow solved to at least prepare your next ingest while the other is on the fly.