What is the "standard 3-rig setup"? The comment on this ticket states that lagging from cyclic constraints can be solved be using the 'the standard "3-rig" setup'. What is the specific setup this is referring to? Is it still considered standard? The comment states that users shouldn't edit the deform rig. How do users adjust the influence of the FK/IK rigs?

I assume that in this setup users are supposed to use copy rotation constraints to get the deform rig to match the other rigs and then to use drivers to adjust which rig is influencing the deform rig. I can't seem to find any finished examples of IK/FK switching that use 3 rigs (on here, Blendswap, Blenderartists). Did something change in constraints or drivers that makes 3 rigs unnecessary?

I am looking for context to understand some of the advice on rigging that may be out of date.
You are essentially correct.

The standard 3 rig setup is as follows:


IK control chain
FK control chain
Deform chain


With the deform chain constrained to both control chains with copy rotation etc, and a driver setup to control the influence of those constraints so only one control chain influences the deform chain at a time.

In blender this is usually done all within one armature, rather than as separate objects, although it could be done separately if you wanted to.

The easiest example to find is the one that comes bundled with blender itself -  the generated Rigify rig uses this setup for arms and legs (Although it has an extra chain prefixed with ORG between the control chains and the deform chain (bones prefixed with DEF), for other reasons).