Typically, Mithril uses raw JS lists, function calls, and objects to create its vdom, which you have to directly manipulate. Like using react without JSX. With a lisp syntax, you might write the end of an expression as )))))), as opposed to in JS, where you might write )])]}); or something similar.
But it's not strictly parenthesis that bother me. You're right in that )]}) is actually far more annoying. I try not to nest that deep in JS if I can help it.
Arrow functions reduce the pain. Not passing array literals in function calls helps as well. Angular seems like the big culprit that injects [] into the middle of an argument list, for me anyway, and using that syntax is optional.
I've actually considered the idea of hacking a JSX compiler to spit out Mithril output.
If you're going to mix mark-up in your JavaScript, may as well do it with "real" mark-up instead of some imitation language. I'm still on the fence about whether I like mixing mark-up and code, but I'm leaning more toward at this point.
It did seem like an obvious thing to do. I probably would have searched for and found this before doing any actual work on JSX, but I'm glad to know it exists already. :)
I personally despise Lisp syntax.