I've done transformations of complex pricing spreadsheets to code for providing dynamic quoting on websites. It was amazing how complex the logic gets sometimes with even what seems like a simple spreadsheet.
I like the idea, but Excel is too damn good and flexible at what it is designed for. It can make many complex things simple, and to match what just one Excel professional can do, you'd have do keep an entire development department.
I know this because we tried it, and it was complete pain in the ass to continuously adapt our "Excel replacing" applications to rapidly changing business/analytics/reporting requirements.
From what I've heard of other Office products, I think the hard part would be keeping my sanity.