I would like to see this as well. I used to use a program call image ingester to do just that. But it is no longer being activly developed and with windows 10 on the horizon I didn't want to invest anymore time into the program. So I bought PM to do my culling, captioning, ingesting and rating. This lack of converting to DNG on ingestation was the only feature that gave me second thoughts about PM.
However, the reputation was so solid and development was on going, so I bit the bullet. I also noticed that with just the mention of dng conversion and exporting settings in the forum, the features were added. That is something I rarely see. I believe I have finally found the missing link in my work flow.
I agree with judophotos. Ingest the raw files to backup and dng to primary storage for use with lightroom.
Although image ingester did a third location it would not be necessary for me. My images are in a folder that syncs with a synology cloud station. This gives me my third and offsite copies.
Jim