I think the current Excel formula language is perfect for what it does. 99.999% excel users don't really need anything more than sum or sumif.

I work extensively in Excel and we have an in-house programming language that can be run with an eval() type excel function. The code is written directly in the cells and you just have to eval() it to run it. It's brilliant, let's you do all you want without breaking excel in any way. The syntax is a pretty standard C variant with a lot of support for matrices (finance work).