If I were Microsoft, I would have a plan for the future for Excel and Power BI, and I would be telling everyone about it. This would be my plan:
1) There would be a basic form of Excel. It would NOT have any add-ins to enable. It would not have any enhancements beyond what exists today. It would work on any device. It would NOT include the Data Model. The new Office apps would work seamlessly with it. Without having any hard statistics, I am guessing that > 98% of Excel users outside of a work environment would be extremely happy with this product.
2) Office 365 – no changes – mainly for corporate use.
3) The new product would be Power Excel. Excel as it currently exists would be integrated with the new Power BI tools. The VBA object model would be expanded so that all of the BI “components” would be fully programmable/automatable inside SharePoint and with other Office products. It could toggle between SharePoint installed on corporate systems and SharePoint in the cloud. An app on any device could access and run Power Excel loaded on a server. The argument against VBA for enterprise applications has always been that the code was not secure and not compiled. Code in Power Excel files would be “protected” by SharePoint, thus making an outside programming solution unnecessary.
So, I would do this and make sure that my customers knew the details of my long-term plan so that they could make timely business decisions based on that information.
It’s probably obvious based on my comments here that I have no inside knowledge of what Microsoft intends to do in the future, but it is my hope that their vision is similar to this.