1 Custom Circuit Per Breaker

Since 2013, the rules have stated that a single “custom circuit” is allowed per breaker, and that breaker may be up to 40A. Does the first part of that rule really have any meaning? Since only a single wire is allowed in a PDP WAGO connector and a “custom circuit” is defined as any electrical component other than the core control system, is it even possible to judge that there is more than one “custom circuit” connected to a breaker? One could easily define a single “custom circuit” as the assembly of multiple COTS or fabricated devices connected together by power wires which then, as a new “custom circuit”, is connected to the PDP through a single wire.

this year we had a camera, network switch, leds, rpi3, and a voltage regulator connected to the same PDP port. inspection was fine.

Seem like a formality to me, maybe?
You could argue that as long as there is a continuous path for charge flow through all of the things you want to connect, that it is a single circuit.

If one item causes the current to spike and trip the breaker, all of them go out. So there is that to consider.

While the glossary defined a custom circuit as a component, it is quite clear that multiple custom circuits can be powered through the same breaker through rule R35, which clearly states that multiple CUSTOM CIRCUITS may be controlled by a single motor controller or relay module, and R56 just as clearly states that a motor controller or relay module may only be powered through a single breaker. Further, the blue box on R56 states that

This implies that at least for the purposes of R56, a custom circuit may be a collection of components.

Of course, the usual caveat that the rules may change next year!

However you do get the benefit of not using a bunch of a limited number of 20A or even 40A slots for 2A loads like the RasPi3.