I think track sacks need to evolve significantly from being EAI Keirin Tote clones. This includes the one I designed for myself:
I think the move should be towards modular pieces instead of "one bag to fit all things".
Making a "version 2" of my track sack is one of my winter projects.
EDIT:
Professional camera bags have made such a quantum leap in the past decade, going from basic box-shaped bags and camera vests to utility belts with modular accessories based on your style of photography and what gear you need to have on hand at the moment.
I'm not suggesting that we go to a Batman utility belt system for track sacks. I'm just using the example from the photojournalist world of a big shift in how things were done that was well-received.
Notice the old style (big rectangular bag) and new style (utility belt) in the same photo (who is more mobile with free hands?):
