The member peering LANs can be found in various variations. Every IXP has its own policy how this will be done, there is no real 'solution' to that, it's rather a decision an IXP has to make on its own.
A very simple approach is to have all unicast and multicast traffic on the same production VLAN.
Some IXPs also decide to have all unicast protocols in one VLAN, and separate all multicast into a separate VLAN.
Another approach is to separate IPv4 traffic from IPv6 traffic on separate VLANs. This means the Members of the IXP must not necessarily be dual-stack, but have a separate VLAN for IPv6. Also very good (and an easy way) if you want to measure the amount of IPv6 compared to IPv4 traffic in your network.
The subject says it all - another - maybe expensive to maintain approach is to have VLANs for every address family. This means IPv4 unicast, IPv4 multicast, IPv6 unicast and IPv6 multicast will all be living in a dedicated VLAN. This option is mainly mentioned because of completeness and is not widely deployed or recommended.