So a simple concept right?
Tunnel your L2 protocols through a switched network? I agree, but as usual, i put more complication into it. Basically a VOD from IPexpert on L2protoco-tunnel used to create a trunk connection. In the video it is shown that you can create a trunk by using a l2protocol-tunnel (STP in particular). Through extensive testing and discussion on OSL, this is possible, but you will only get the native-vlan traffic through.
I will assemble my thoughts on this and elaborate with some diagrams shortly. But the conclussion will still be the same. If you need to pass data from more than one vlan over a switched SP network, use Q-in-Q. Use l2protocol-tunnel to pass the L2 protocols, CDP, STP and VTP, but dont rely on it for anything else.