Michiel wrote (2021-02-01):

 MvdV> *) Coming to think of it... Full IPv6 connectivity is better of course,
 MvdV> but when having to choose between "OO" and "IO", Outgoing only is better.
 MvdV> While in the near future we will see nodes that are connectable via IPv6
 MvdV> but no longer can accept incoming IPv4 (INO4), alll these nodes will stay
 MvdV> have outgoing IPv4 for a long time. So your "OO" node can still have full
 MvdV> two way connectivity with those "INO4" nodes. An "IO" node only has one
 MvdV> way connectivity with "INO4" nodes.

If you only have IPv4 connectivity you can still use a Tor proxy (or some other proxy/way) to connect to IPv6 nodes. Adding incoming IPv6 is much harder.

Btw, what's the point of OO only nodes in the list? I'm sure many more nodes can connect over IPv6 nowadays.

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