My vote goes for a tabbed onebag look, i used the invsort until it was so broken i had to abandon it.
I´m trying to wrap my head around what the hardest part of this addon is.
tabs with the regular categories, then atleast 1 custom one we can define ourselfs, add the option to open the tabs 1 by 1 just like when we open diffrent bags, and combined with your sorting eng i´d be a happy man.
i can´t see a need to make it more complex than that, but i guess others see it diffrently. :)