Oh I'm sure you do, but it popped into my head as I typed the start bit, so I thought I'd share. It was just a thought, and a lot of work to do before finding if it works or not. Probably the closest to a spriter type effect you will get with iso 3D. I'm not sure how you do your graphics thought. They look hand drawn, but may be rendered. If you are using a 3D object to grab from, you could hide all but the limbs you want to see when grabbing from within DB and auto gen them.
I did a little util like this, just minus the limb feature, but it would have been easy to do. I lost it in a HDD crash and have been meaning to re-make a better one. I just haven't got round to installing DB yet ( about 4 months now at a guess, since the crash, maybe more) and have been too busy with other projects using AGK. Plus I haven't needed 3D grabbing since I lost my iso engine. Something like that would certainly help you out time wise. I'm not sure if sprite me, et al do something like this already. I would imagine so.
I used the mirror technique in my old demo also. It saves a fair bit. I remember talking to you about it before. I'm unsure what you mean by retina resolution (960x640, 1024x1024 or 2048x2048?). How big is each sprite frame? I really think you will have to reduce it down as far as you can get away with if you are as low on memory as you say. I have no idea how much my apps use, but Obliterator is the biggest image wise so far and apart from when things get busy, I'm keeping speed up at the moment.
best of luck with this anyway, it looks really impressive!
@ Zdaxxy, what are you stuggling with? I have made a simple picture to demonstrate the grid process I used. The green blobs denote the pivot point of the sprites. There are probably various methods, but I used a 2-1 x/y ratio on my grid, so for example 64x32. That way you can tile the segments together nice and easily in a loop. I had never read up about iso in any way, I just worked out that this looked an easy way to do it (by messin in a paint package), and then went to work in AGK. I dealt with z depth by using the y height of the sprites feet compared to the exact center of the scenery sprites. It worked better than I hoped at the time, pretty much perfectly. Hopefully you have a few ideas there to help you along a little.