I have used Kifaru packs of various shapes and sizes with no issues over the years. The only time I would see it as an issue is if you were in a late boarding group and the overhead bin space was full, because they likely would not let you put something that long under the seat in front of you. That means gate check, which could present some of the issues outlined above. I like to put my optics (or anything else expensive and breakable) in the lid, so I can pull it off the pack and keep it as a carry-on in the event I had to check the pack.
If I was going to mindfully check the pack, I would definately put it in a duffel of some sort to protect the buckles, etc. as described above. We got into camp last July in the NWT and the load lifter strap of another hunter's pack got stuck in the seat rail and a loose seat wore 2/3 of the way through the webbing.