And the answer is mixed-mode VC vs non. In a mixed-mode VC the default forwarding class set is the five classes as seen in switch2 above, with a regular VC having eight.
This is odd behavior given that a mixed-mode VC will drop features down to the lowest common member capability--which the EX4300 already is.
Mixed-mode:
test@switch> show virtual-chassis status
Virtual Chassis ID: xxxxxxxxxxxx
Virtual Chassis Mode: Mixed
Mstr Mixed Route Neighbor List
Member ID Status Serial No Model prio Role Mode Mode ID Interface
0 (FPC 0) Prsnt xxxxxxxxxxxx ex4300-48p 128 Master* Y VC
Member ID for next new member: 1 (FPC 1)
{master:0}
test@switch> show class-of-service forwarding-class
Forwarding class ID Queue Restricted queue Fabric priority Policing priority SPU priority
best-effort 0 0 0 low normal low
fcoe 1 3 3 low normal low
no-loss 2 4 4 low normal low
network-control 3 7 7 low normal low
mcast 8 8 0 low normal low
Non Mixed-Mode:
test@switch> show virtual-chassis status Virtual Chassis ID: xxxxxxxxxxxx Virtual Chassis Mode: Enabled Mstr Mixed Route Neighbor List Member ID Status Serial No Model prio Role Mode Mode ID Interface 0 (FPC 0) Prsnt xxxxxxxxxxxx ex4300-48p 128 Master* N VC Member ID for next new member: 1 (FPC 1) test@switch> show class-of-service forwarding-class Forwarding class ID Queue Restricted queue Fabric priority Policing priority SPU priority best-effort 0 0 0 low normal low expedited-forwarding 1 1 1 low normal low assured-forwarding 2 2 2 low normal low network-control 3 3 3 low normal low mcast-be 8 8 8 low normal low mcast-ef 9 9 9 low normal low mcast-af 10 10 10 low normal low mcast-nc 11 11 11 low normal low