What I was looking for is something that mimics the Edge tab set aside feature. This comes really close, but the one thing that keeps it from really shining in my opinion is the ability to open individual tabs that have been set aside. Otherwise, this is a really good start; thanks for making it!

Update 2017-12-20 for 1.13: Added a star (up to 4 now) for the ability to open individual tabs that have been set aside. I'll update to 5 stars if you allow for removing individual tabs from a set-aside group as well (so that if I have several tabs but want to set them aside and deal with them one-by-one that'll be easier), and as a nice-to-have, it would be great to be able to have an option to open and remove from the group at the same time (and maybe an option to make that the default behavior). It's coming along nicely, though, and with this update I can make it a bigger part of my workflow. Thanks!