Well, if you are game for "wish list" ideas...
A way to stack a sortainer on TOP of a T-Loc might be nice.
I like putting the bigger systainers on the bottoms of the stacks because I store these in the basement, and if we get water in the basement, the bigger systainers will generally protect their contents until the water gets to the level of the crack in the lid. Using a SYS4/SYS5 on the bottom of the stack means the water needs to get a bit higher before I risk losing things. With the sortainers, this still works with the "classic" systainers on the bottom, but the T-Loc ones would force the drawers to be on the bottom - in which case their contents would get flooded first.
I have enough classic systainers that this is not an issue for me right now, but I suspect as time goes on and the "collection" grows, this will become increasingly problematic unless the sortainers are redesigned to stack on top of the T-Locs or some other method of dealing with this presents itself.