There will also be Wolfram Desktop, the local IDE for the Wolfram Language that comes with our online products, as well as Mathematica 10, a non-cloud-enabled instantiation of the language for the academic market.
If you want notification as soon as we go public, sign up on http://www.wolfram.com/programming-cloud/.
Disclosure: I deployed this code from my own copy of a prerelease version of Wolfram Desktop, which I could do because I'm an employee.
P.S. Your idea of being able to write Wolfram Language code straight into Alpha and have it execute is an interesting one. You can do some basic stuff like http://www.wolframalpha.com/input/?i=Table[i^2%2C+{i%2C+1%2C...] already, but I agree we should allow you to execute anything (safe) using Alpha.