Agree. RSK may never replace Ethereum no matter how hard it tries. But at least, it could complement Ethereum in many ways. Being "attached" to the main Bitcoin blockchain, brings its benefits. The RSK blockchain can enjoy greater security and reliability unlike any other smart contract platform in existence today. At least, that's an advantage RSK has over its competitors. With different smart contract platforms in existence, the competition gets tougher day by day. Each have their own features and unique use cases for the mainstream world. Since Ethereum was the first smart contract platform ever created, it has obtained first-mover advantage on the market. At this point, it's nearly impossible for any other smart contract platform to take over ETH's place as the world's second-largest cryptocurrency by market cap.
Even Binance Chain was hailed to be the next "Ethereum Killer". But what matters most is mainstream adoption and real use cases instead of the technology or features of a smart contract platform. Binance Chain may be faster and cheaper than Ethereum, but it's way behind in terms of mainstream adoption. Same applies for RSK, Cardano, EOS, and any other smart contract platform created to date. Despite this, I believe that the future is bright for alternative smart contract platforms like RSK and EOS as they provide unique use cases for the mainstream world. Some businesses or companies would prefer a platform that focuses on security above all else. While others would prefer convenience (greater speed, lower costs) above all else. With so many options to choose from, I believe that each smart contract platform will shine on its own.
That said, RSK is still an experimental platform not ready for mainstream use. Cardano is in the same path, so I think we're still early to talk about them. Whenever RSK will prove to be successful in the long run, it's yet to be seen. It's an interesting concept that proves the power of sidechains on the Bitcoin network. Since RKS is widely compatible with Ethereum's Solidity programming language, developers could easily migrate their dApps into the platform to enjoy a greater level of security/reliability than Ethereum. Whatever the case may be, RSK could experience greater adoption once it's finalized for mainstream use. Just my opinion