Just saw this post come past:

http://blogs.technet.com/b/windowsse...and-cloud.aspx

If you want to target cloud then running your webapp on a Windows nano server sounds like an interesting option.
However .. note this quote (emphasis mine):

Nano Server will allow customers to install just the components they require and nothing more. The initial results are promising. Based on the current builds, compared to Server, Nano Server has:

93 percent lower VHD size
92 percent fewer critical bulletins
80 percent fewer reboots

To achieve these benefits, we removed the GUI stack, 32 bit support (WOW64), MSI and a number of default Server Core components. There is no local logon or Remote Desktop support.
I'd imagine that adding 64 bits support to just the webapp stack would be as good a start as anywhere and it would certainly make sense.

--
Wil