Yes, GUN is again trading on Cryptopia. And more good news we just release V1.5.3. It will block access to old clients on the network.
does it block v1.5.2 clients too?
because until/when cryptopia and otherplaces like prohashing.com update from 1.5.2 the new wallet wont be able to receive from them.
No it does NOT disconnect from V1.5.2 and should not. It is not a matter of what code they are running, it is a matter of whether they are using Segwit addresses or legacy addresses. As long as everyone is on V1.5.2 or V1.5.3, there are no operational issues. V1.5.3 will automatically disconnect from older wallets and V1.5.2 can be manually made to disconnect from them. But V1.5.2 and V1.5.3 should interoperate fine together.