There is a extensive JSON API available here [1], which I'm assuming this Excel API will make use of. And we already have this functionality in Google Sheets, so it's not exactly something new. It will be good to see more use of the API though, and interesting to see if they maintain this in the years to come. Perhaps them making a Excel extension will cause them to spend some time fixing all the things that have been broken with the API for a long time [2].

[1] https://esi.evetech.net/ui/ [2] https://github.com/esi/esi-issues/issues