I wouldn't be. The energy is in O365 at the moment, isn't it? VBA is the big programming environment at the moment and it's basically VB6 and hasn't been touched in a long time. There's also that JavaScript thing, which I think is still pretty half-baked.
The JavaScript office API looks like a good solution for integrating your UI within the app. It’s still quite limited in terms of heavier capabilities, eg data processing etc. That’s probably because right now MS is focused more on a shared plugin API for all office products than on deep integration of any one specific product.
