What about just cutting the lid off and taking the bottom and dropping it into like a Systainer or a Bosch L Boxx?
Both the top and bottom of the case have depressions that holds the pieces in their place. If I put them into another box the height would have to be just right or else it would just be a mess inside a mess inside a larger box which is a bigger hassle than just a velcro around the handle or a strap around the entire case. Besides, using a bigger case will require sacrifice in the foot print. I don’t want to dedicate this much space for a set of hole saws.
I might look at just combining all hole saws into a single bigger box though and forget about having them being nicely arranged by size. Right now I have two sets of wood and bimetal (in boxes), one set of carbide (in box), one set of diamonds (in broken box), a miscellaneous hodge podge of diamonds (no box), May be I can put them all into a bigger box, I don’t know, the arbors and bits and accessories would be all over though.