I remember seeing Mint quite a few years ago. I love the idea, I really like the language design, but I agree 100% with your take on the drawback. It's hard to sell that to teams.

What's surprising to me is how many alternatives exist in this space. Between elm, imba, svelte, and mint, and probably more that I don't know about, I wonder how many devs in the world are shipping to prod using them.

edit: have you thought about including Form Validation to the core lib?