i have it kind of working here but this whole variable font mechanism is ... well ... Thank you for your efforts.
I've been playing around on opentype.js.org and they have the problem that both the top and bottom diacritics are not scaled, then for each font. If I set aalt under the fontfeatures, then the document cannot be created, or it would take forever, unfortunately I don't have that much time. hm, in context? It was supposed to be a wild collection of clues that I thought might be useful and does not have to be related.
1. opentype.js.org (the Glyph Inspector to be pecise) has comparable problems, and show informations about composition of the glyph. It was helpful for my understanding. 2. aalt is an independent problem that occurs in context. The process stalls and must be cancelled manually.
The features that should actually be on by default are not, for example Kern, but I'm not sure if that's intentional. you need to take them from default :
\definefontfeature[foo][default][....] in tex it's all ahbout control so no hard coded defaults Yes, actually obvious, but I didn't think of it myself.
Translated with DeepL.com (free version) so is this a human or bot speaking here ... A human, I use deepl as a little helper because my english is ...well... good for reading technical documentation and not much more. The attachment wasn't intended.