I expect for this year, Rootstock (rsk), lightning, Schnorrr, Mast, Atomic swaps.
Schnorr is a softwork not a sidechain, and most important Rootstock is almost out and is in beta right now which is the last testing phase.
Rootstock has been in development for a very long time, and will bring Ethereum to the bitcoin. Which means Ethereum prices will drop
drastically.
More projects will come for 2018-2019+
You need Bitcoin for the use of blockchain, Bitcoin is the payment app. You can make alot of apps for the blockchain, you can also call these
apps sidechains, or 2th/third layer and drivechains. Bitcoin can only go mainstream with these sidechains forget blockchains.
Bitcoins potential is very huge and for sure can replace the monetery financial system. I don't know how much % but 1% penetration will make
btc 100k+ for a coin.
https://media.rsk.co/rsk-brings-the-new-evolution-of-bitcoin-reliable-smart-contracts/Eversince, I've believed that there are more years for bitcoin's success specially that there are many countries as of now are engaging with bitcoin. A lot of future projects will be made and bitcoin will be used in different things. The era of cryptocurrency is just started, we will see the bright future of it more years from now.