Do you want to popularize Office JS Add-in development? Why don't you do as you did with VBA? There is a macro recorder and the VBE (VBA's IDE).
Anyone with a regular Office instalation can be a "developer" - just press Alt+F11 and start coding. This is a great incentive for begginer programmers.
If you recluse Office JS programming to Visual Studio it'll be no use even if the framework is great, because there'll be no adoption by the community.
You have to tease your customers' mind so he'll get addicted in macro recording and will want to learn more about office automatization.
That being said - I believe that providing an IDE for Office JS Add-in development should be a priority in the roadmap.

I understand that the compiling and deployment of Office Add-ins are a whole bunch more complicated than compiling a VBA project - that's why we use Visual Studio. However, in the worst case you could limit applications's IDE's capacibilities (for example, you can create Office task panes and Office-level add-ins using VB6, but can't do that through VBA).