I'm completely opposed to your idea, here is why:
I'm an operating engineer, and I have to troubleshoot and repair 40 year old stuff as well as operate it.
Things Fail. Obsolete stuff must be replaced. Neat new stuff is too cool to ignore.
Hidden stuff is hard to get to, hard to troubleshoot and hard to replace.
I like your idea of a simple VFR ship, I built an RV-8 with that as my goal.
BUT, I ran wires from the right console, thru the gear tower and thru the baggage well, and mounted the battery on the firewall, with the filter capacitor, battery contactor, gauge manifold, fuel filter and fuel return regulator on the firewall where I can easily access them. (Battery and electric system back and up the right side, Fuel system up and back the left side)
I put the electric fuel pumps in front of the left gear tower, and dread replacing a fuel pump when the time comes, heck, it's hard enough to clean this area.
My RV-8 is no show plane, it's rather plain, unpainted dull aluminum and DP-40 on fiberglass, but it only weighs 1034 lbs empty and flies great! (I didn't even convert to aluminum gear legs!)
You could run the wires below the longeron and drill holes in the center of the longeron flange for zip ties or lacing cord to hold the wire bundle up out of sight.
The Glory of an Experimental Aircraft is the freedom to change it. I'm in the process of removing engine gauges and installing an EMS, so my accessible wiring is going to be butchered again.
Hey; I'm adding 'lightness'!