Wooden version will be useful for junk trains mod. It allows building trains much earlier and cheaper, so steel is expensive.

Wooden version should have less capacity.
If you think this is OP, you can make it as an setting.

I've made graphics and code for your version 1.7, i'll send it to you with PM.

Unless you modify 1.8 code it would do no good. Steel chests are so hard wired into code that changing it will be possible but it will also be massive pain in the ass. I will think about it but if I do this then people will want also iron chests to be able to merge...

I've done wooden version for 1.8.3.
Also I added support for "bar" (red thing to limit space in chests).
And also added support for circuit connections (not ghost, but at least I can merge and split the chest again, so it's possible to store split version in blueprint and then just merge it manually).

I'm thinking about adding "Merge Trigger" entity as a workaround for blueprints (before they finally publish API for ghosts).

The sources:
https://drive.google.com/file/d/1uqiXxXpZn27lDsj2FLtMoB514KgCDezX/view?usp=sharing

Oh, you have done circuit connections here. Ok I will look at it when I have the chance.

I left in 1.9.0 release possibility to change mergable chest type. Uncomment in lookup.lua, replace chests sprite, change mergable chest in mod settings and you are good to go. I will wait for next release to enable this option for everybody (when i got the sprites).