You can pretty much already do what you want with VSTO or XLLs. However having a standard scripting language installed on everyone's machine is a all different thing. It means you can add some scripted logic in your spreadsheet, give it to someone else, and know it will run without having to install or maintain anything.
This is incredibly important. When I worked at BigFinCorp, we always used vanilla Excel (VBA and ODBC to RDBMSs). So our sheets would always "just work".
Python would be great in this role, but to avoid separate configuration, you'd need to ship the runtime with the spreadsheet, right?
Or would this new Excel capability be built on .NET? In that case, C# (for the enterprise folks) and F# (for the bleeding edgers) would be fun, too.
Bottom line, the Developer mode of Excel should support more than VBA.
