Codex, I used ABP for a long time. I had lots of chats with the guy who took it on after ABF was abandoned. I'm the one who did most of that ultrabag idea.
And after lots and lots of thinking and working hard to try to get UltraBag to be something usable, I just stopped caring. EngInventory seems to cover almost every "good" idea I had for improvements on ABP, and ABP was a huge memory hog. I just can't get myself to make it, given how hoggy it is. Maybe if I find myself with tons of free time at some point, I'll start thinking about it again, but the closest thing to ABP we're likely to get is Ramble's MyBags in a future release, when he makes it so you can hook other things on top of it, and I put in a filtering system. Which will basically be half way between OneBag and ABP -- you get one bag, but can apply arbitrary filters to it. So if you want just your herbs, you can look at just your herbs, but you can't have multiple windows open at once, and all that jazz. That was the big memory waster.