There may not be one single dominant blockchain network in the future, thus, will blockchain start to interoperate in 2018 
What do you mean by interoperate? SegWit activation has paved the way for cross-chain atomic swaps, in which some amount of BTC is exchanged for another coin P2P, with no transactions recorded on-chain.
This has been demonstrated with several SegWit coins, such as LTC and VTC.
https://bitcoinmagazine.com/articles/lightning-network-now-supports-transactions-across-blockchains/
^This
You may want to clarify exactly what you mean by interoperate