This sounds like a really good idea - combining spreadsheet convenience with being able to do programmatic manipulations with python can be really value for people who are using spreadsheets to do modeling (e.g financial). I think (especially based on some other comments) a big challenge will be just getting people out of their current bubble. If you do financial modeling, you might be entrenched in excel, and if you so data science in python, you might never dream of using spreadsheets.
My unsolicited advice (that's probably on your radar anyway) would be to try and get a management consulting firm on board with this. The flexibility this has would be well used there, and you've got lots of people who are engineers stuck using spreadsheets that would be on board with trying something like this.
Our biggest challenge as you say is definitely the fact that lots of users will be entrenched in Excel. Our goal right now is to appeal not to those who are happy in Excel today, but to those who have grown disillusioned: lots of users today build up amazingly complicated things in Excel and grow frustrated by the difficulty of maintaining that complexity. Python can be a much better fit in many cases for a lot of that complexity.
And as a platform for data science, we've found Neptyne really nice for sharing results. I was surprised at how often I heard from users: "well, we usually do everything in Jupyter, but then whenever management wants to see the output, they ask for it in a spreadsheet".
My unsolicited advice (that's probably on your radar anyway) would be to try and get a management consulting firm on board with this. The flexibility this has would be well used there, and you've got lots of people who are engineers stuck using spreadsheets that would be on board with trying something like this.