Re: Post your SegWit questions here - open discussion - big week for Bitcoin!
Sigh, read achow101's post if you wont read mine 
You WON'T connect to non 0.13.1 nodes.
Yes they CAN connect to you, but you blacklist making connections to them, since they are 'different'.
Actually technically that isn't entirely true either. 0.13.1 will still connect to nodes without the relevant services (i.e. no NODE_WITNESS) under certain circumstances. Right now that is 40 failed connections and having less than 4 outbound connections. Otherwise yes, it won't connect to nodes without the relevant services. This behavior is not limited to just segwit but in general for node services; it just happens to be that segwit is the only major node service right now.You WON'T connect to non 0.13.1 nodes.
Yes they CAN connect to you, but you blacklist making connections to them, since they are 'different'.