Btw, why not inserters combinations?
Preface by saying I'm not the dev...interesting idea, but have you tried any of the loader mods? I use Loader Redux and it has been great. I've taken to setting up a merged chest the length of my train (4 tiles away...loaders are 1x2 and you need 2 of them...one to unload the train and one to load the chest) and then place a pair (up to 6 pairs) per car instead of inserters. A base level loader (yellow belt equivalent) is slow, but still generally faster than the mid level inserters if you use multiples. And if you did something like say 6 express loaders (blue belts) you can completely unload a full car of high stack capacity items (like copper wire at 200/stack) faster than the fastest inserter (vanilla...haven't loaded any mods with higher levels). Never timed it but talking seconds.
In terms of adding other sizes, I wouldn't mind some smaller ones like 1x2 or 1x3 myself but for my play style (and installed mods) they also wouldn't drastically change anything. In most cases I'd use it to feed to or from multiple assembly machines and for that I downloaded a mod to allow inserters to do 90 degree rotations (I've seen mods that allow other increments as well) instead of the default 180. The end result I can get the same result with a standard 1x1 chest. If I fill up the 1x1 chest, I probably have enough back stock for my purposes and don't need the extra space afforded by the merged chest.
Just a couple ideas for you to try if you haven't looked at them already. Hope they help you out.
