www.makemkv.com

I'm currently ingesting my entire DVD and Blu-Ray collection into Plex by using Make MKV. I have over 1000 titles to do...

Now here's my naive question.
Is it possible to add a second BD drive to my iMac and double my rip/ingest of movies? Can I in effect have 2 different Make MKV sessions running independently of each other?

Yes, and you can add even more than one...

There is a new feature in MakeMKV that, if you have more than one drive, it will ask on start up which drives you want THIS COPY to manage. This makes it easier for dealing with multiple drives.

Awesome! Would I run both sessions from the same window or would I open a second window with another separate Make MKV session?
Hope that makes sense...

Each is a separate instance with its own window.

On mac, there is a "New instance" item in the menu.