> Well, I was tempted to mention Haskell. Problem is, I haven't found a practical use for it.

That's the same as saying:

Well, I was tempted to mention Go. Problem is, I haven't found a practical use for it.

That is to say, just pick a problem and try to use Haskell to solve it. 90% chance it will fit your niche fine.

Depends on how you define "major". Dropbox is currently running Rust in production, at the core of their product. Has been for about six weeks now. That's probably the largest, most serious use. There are also tiny bits in Firefox, that will be included starting with the next release.

There's a lot of other usage too, it all depends on how you define "major".