Hmm, I may take a stab at it. I use Google Sheets for most of my existing stuff (asset allocation calcs, Roth basis tracker, tax worksheets, etc.). I've never done anything this fancy, but I'm sure I could learn.
Through work I have access to Excel, but no guarantee I will always have that at future jobs, so I wouldn't want to build anything in it. Maybe OpenOffice/LibreOffice if G sheets isn't cutting it.
There is already a lot of good work out there, I may also look at the source of cfiresim since it's open source and on GitHub. It shouldn't be that hard to add in support for a bond tent type thing.