The build video is somewhat amusing to me. The crowd was WAY into the REPL demo, wherein they showed things that any dynamic language has been doing for decades, all the while trumpeting the "power of static typing". There IS power in static typing, but by the time you're in the REPL you don't need much of it.

Intellisense in a REPL based on static type information is novel, as far as I know. Some dynamic languages do this based on dynamic type information, but that is limited to expressions whose value is known. For example you have a variable A in scope at the REPL, and it has a method A.foo(), then you'll get completion on .foo. But you'll not get completion on A.foo().bar(), because the value of A.foo() is not known at the time of typing that expression.

I dunno, the reliability of Intellisense static typing gives combined with a REPL would be even more useful for exploration.

That aside, it's exciting to have the ability to have both.