I didn't get the impression from that article that "replace the native implementation with a JavaScript implementation for better performance" was the goal at all. Rather, the goal seems to be "move away from a situation where one holdout browser (traditionally IE, more recently Safari/iOS) could scupper a new feature completely, and toward one where holdouts are just slower if they don't support that feature natively". There have been lots of examples of that strategy working - jQuery/QSA, asm.js etc.
Is that a misleading impression? Does Houdini have another agenda not covered by the article?
No, that is an accurate impression. The ultimate goal of Houdini is to give developers the tools to innovate; unlike the current situation were all innovation happens at the spec level, and devs have to wait (often years) for browser adoption.
That's accurate, and totally reasonable. If the web is going to move forward, there needs to be a certain acceptance that older browsers should work, but they don't deserve to work well.
And definitely not as well as the latest and greatest.
Is that a misleading impression? Does Houdini have another agenda not covered by the article?