It's also likely to be inherently hard to optimize; aka slow and will stay slow. I thinks it's a generally bad idea. It also undermines what limited tooling there is for JS; and it exposes Yet Another set of semantics - what exactly does that query do, how is it translated, what are the corner cases etc.

Very Bad idea. (And for what - avoiding a few characters that are so common as to be trivially skimmable and very gzippable?)

What do you think about jquery selectors? Do the same objections apply?

I think they do too. I used to fall-back to vanilla DOM queries sometimes when I started using jQuery, because it didn't feel quite right, and I always worried about the performance hit... but I ended up always using CSS selectors, unless there's a good reason not to.

I think the main difference is that the value proposition of CSS selectors is just better than of the string-function syntax, so its worth it.

CSS selectors also give me this bad feeling when used in javascript code.