Is RSK going to be implemented on bitcoin only? Is RSK going to be implemented on bitcoin only ? The other hard forked bitcoins, i.e. bitcoin cash, bitcoin gold, B2X, bitcoin diamond will not have RSK implemented on them, am I correct ?
That would depend on the devs of said fork. (And the devs of RSK aswell probably)

I for one have not really looked into who supports what, but a quick google search hinted me that Bitcoin Cash for example, (https://twitter.com/viabtc/status/896016235816562688) might have interest in implementing RSK aswell.

I wouldn't be so quick to argue that this couldn't / won't be implemented in other bitcoin forks.