I actually used a USB connector on the previous Nixie-tube based version. It's harder since there aren't as many panel-mount options for the USB connector. You have to design the circuit board around abutting the enclosure wall. This makes sense in an injection molded or unibody construction, but less so with a wood box like this.

You're also potentially limited by the USB spec on current draw. There are ways around this, like ICs that will detect if you're connected to a charger or a data port. The barrel connector is also quite ubiquitous and I designed the power entry to work across a wide range of DC power adapter voltages.