Indeed, pretty kewl. But EVERY DAW in the world was able to create stems. Stems is not something NI invented, they just marketed it cleverly and probably registered it as a “product name”.
Stems is a term long used by (especially mastering) engineers.
When supplying your track for mastering you could either hand over the full multitrack recording (tracks), stereo (obvious) or stems. In this context stems is nothing more than a group of tracks bounced to a single audio file. For example, all drums would make up one stem as well as the brass section, etx.
So when in Logic it says create stems, it’s nothing to do with Native Instruments or the new “open” STEMS format.
I understand the choice by NI, but they did introduce some confusion into the (pro engineering) community. Creating STEMS will be different from creating Stems, if you get my drift!