First-class integration in Excel would be a game changer. Holy shit. Though adding a multiline editor with indentation in Excel would be really nice as well. We've got to stop pretending Excel functions don't constitute a programming language.
The finance folks I work with are fucking wizards. I'm convinced many of them would have made great engineers given what they can accomplish building applications in what might be the world's worst IDE.
I'd say two things would make it better: - Have a "code" version of the cell editor that has formatting/indentation + basic linting. [Sometimes 75% of the challenge is reading the code in linear fashion and figuring out what it does]
- Integrate git-like versioning and some sharing features with Office365. Basically, make it so that you can roll-forward or roll-back on both the code and the contents, and make it so that you are _not_ emailing files around to share them.