The whole s/X/Y/ thing is very Unix, and is a (sub)cultural signifier as much as anything. I'm not sure if it's originally from ed, sed, or what, but most people (self included) probably picked it up from vi (nvi/vim/etc.) or perl.
X->Y makes just as much sense, but the s (for "substitute") makes it mnemonic - I read it as "sub X for Y".
Well, right, but how many people here have actually used ed standalone? (lone hand) It's overwhelmingly likely that most people picked it up from vi(m).
"thing" → "other thing" is the same length, and while not natural language, it isn’t a computer language.
I think using the sed-like (right?) language is more useful as a signaller. Check it out, yo, I grep shit all the time.