Users of smart contracts will pay a fixed fee, i think its around 0.001 Waves (no GAS required like with ETH, or NEO). This fee will go to the nodes, (Waves has no miners like with ETH). The more mass adoption, the more transactions on the platform, the more fees for the nodes. You can start your own node with 1000 Waves, or lease your Waves out to another node to earn rewards. Smart contracts and Atomic swaps will contribute to the mass adoption because with will enhance functionality for users. For example, it will allow ERC20 tokens to be traded on the DEX.