Some languages understand λ directly (and in all lisps that support unicode, you can explicitly alias it) - I've occasionally mapped AltGr+L to λ, when playing with those. It's really nice.
APL perhaps goes a little far, but I'd like to see more standardized symbols in programming languages. Imagine how nice it would be to succinctly use things like the actual outer-product operator ⊗...
When I learned APL long ago in a languages course, it was on a dedicated APL setup with an APL keyboard.
In that context, it was a "how SHOULD things be" sort of design decision. I know I started off quickly thinking in terms of math and the language, not composing symbols.
Of course, APL keyboards have gone the way of the dodo and so the language has a higher barrier to entry.
APL perhaps goes a little far, but I'd like to see more standardized symbols in programming languages. Imagine how nice it would be to succinctly use things like the actual outer-product operator ⊗...