Someone just created that!

https://excelformulabot.com/

Apparently Microsoft is creating a plugin.

(Not affiliated)

Not quite what I meant. Basically you fill in some cells, and then expand the region and Excel will autofill. For example if you have

    Full Name        | Nickname
    Smith, John      | Johnny
    Ayers, Danielle  | Dani
    McDougle, Jack   | Jack
    Jason, Charles   |
    James, Trent     |
    Myers, Jessica   |
    David, Katherine |

And if you select the first 4 entries on the right and drag down, it will fill in the last 4.

This is known as flash fill and already implemented: https://support.microsoft.com/en-us/office/using-flash-fill-.... Except AFAIK it still uses hard-coded pattern recognition. This is exactly the type of thing ML is good for!

Google Sheets has this and it works really well.

I had an idea Excel had something as well but maybe not?