I am all for using S2 wherever possible, but it is very unlikely to greatly change things by itself for an unstable network that doesn’t use S0
After going through this, I have to agree with @mundschenk-at - the conclusion is that S2 is less overhead than S0, not less overhead than no security at all…
Also, I’m not sure what’s going to happen to a network with lots of hops when only some of the nodes utilize security.
Nothing, the message is fwd to the node just fine.