There has never been in the history of bitcoin that a hard fork bitcoin has ever become successful, the ones they did in the early days of bitcoin and the ones they did in the all-time high price of bitcoin to date have not reached the half potential of bitcoin
A hard fork does not necessarily imply creation of a new shitcoin, such as in the BCash fork. It is possible to implement a hard fork which the entire network agrees upon, which results in everyone staying on the main chain and no chain split. A hard fork simply means that the rules are being relaxed, and something which was previously invalid is now considered valid.
As an example, I believe block 74,638 back in 2010, well before my time, technically resulted in a hardfork. There was a serious bug which broke the 21 million BTC limit. The bug was swiftly patched and everyone switched to the new software version. That fork would clearly be considered "successful" because it fixed the bug.