This would be highly valuable to me. Right now, it's possible to set content via a Javascript Ternary in Expression. I'd like to be able to have a custom JS fuction with param(s) and call that in the Expression to set the content. I can imagine many uses cases but the most immediate for me is being able to have complex logic based on the query string. Specifically, I'm building a landing page for Google Ads. Google rewards landing pages that are highly relevant to the ad and the keyword. Google allows us to pass as query string details about the ad and keyword. I want to capture the query strings and run through a series of If and/o switch blocks so I can customize the headline and initial paragraph. Maybe even the hero image. The logic would need much more than simple ternary.
I think either one would be fine. The main goal is for the user to instantly feel the LP is exactly what they were looking for when they clicked on the ad. I don't think there needs to be an SEO or crawler-capable version.