Apparently, the research literature calls this feature Sheet-Defined Functions (SDF). Doesn't it use this result from Microsoft Research UK that was just recently published in ICFP 2020:

Elastic Sheet-Defined Functions: Generalising Spreadsheet Functions to Variable-Size Input Arrays

https://icfp20.sigplan.org/details/icfp-2020-papers/46/Elast...

Fastest beeline from research lab to the end-user I've ever seen.