I suspect the Hindley-Milner type inference algorithm probably showed up in the early 80's, since ML had it, and I was taught Standard-ML in the 84ish timeframe.

Of course there may be pre-ML work predating even that.

"type inferencing as used in haskell et al, that's a fairly recent development - early 90's/late 80's?"

According to the wikipedia page (http://en.wikipedia.org/wiki/Type_inference#Hindley.E2.80.93...), it dates back to 1978

Hmm,

It seems like that might be the next transformational idea, since it hasn't transformed mainstream language yet.