It greatly depends on your overall plan for your build. If you are doing a straight-forward build according to Van's basic design, then very little needs to be done in the tail cone. Conduit would be about the only thing I'd suggest. But some additions may have implications for the tail section and are more easily handled while assembling than after. Trim servo for the rudder? Auto pilot for elevator and/or rudder? Air conditioning? Oxygen bottle? Depending on how you intend to equip, you may need mounts for an AHRS, magnetometer, strobe drive, and ELT. And some of these may conflict with each other.
I modified the battery mount for a 24V system which, together with the pitch servo, left no room for the AHRS mount. I could have reversed the design to put it on the other side of the battery, but I already had the mount for the O2 system there. The next bay back was taken with the intake and outlet plumbing for the air conditioning, and the ELT on top, so the AHRS ended up in the fuselage under one of the rear passenger seat pans. With so much equipment in the back, I elected to put the magnetometer in a wing tip. And, I built a trim tab into the rudder as I assembled it.
So, you can see that your equipment plans may affect what you do. People will tell you not to plan the tech too far in advance because it changes and, to an extent, that can be true. But many of the items I mentioned don't change that much (air conditioning or O2 system) while others are fairly standard (strobe drive, servos) so the decision is not what but rather will you or won't you use them. Other things that may be specific to your panel can be decided later but you still want to leave room for them and plan conduit runs.
I had difficulty installing some items into my RV-6A because I didn't decide to add them until after the airframe was built. On the -10, this caused me to over-plan, which caused me some heartache when the VP200 became obsolete and I had to redo the panel. Learning from both experiences, I think a happy medium (whatever that might be) would be the best approach.