Maybe the real problem to solve is not killing Excel but providing a pathway for load-bearing Excel sheets to grow into full applications, development practices and all.

I feel like this is doable with a good LLM-assisted coding tool, but it's just a hunch.

I think the hardest part here is UI.

With Excel you get no-code immediate UI feedback in the cells.

Most people will use an Excel sheet as an array or a dataframe.