SMuFL: rotated arpeggio glyphs?

Hello,

In my work on making the Emmentaler music font SMuFL-compatible, I've 
found the way SMuFL encodes arpeggios a bit hard to grasp.

The arpeggiato segment glyphs (/wiggleArpeggiatoUp/, etc.) appear to be 
turned on their side, meaning that programs would have to rotate them in 
order to use them. However, I can't seem to find how this is to be done 
in the specification. Does SMuFL dictate how programs should place 
arpeggios? If so, how?

In addition, a fellow LilyPond contributor has brought up that there are 
other, better ways to encode a vertically tesselated glyph (see this 
message on the lilypond-devel archive: 
https://lists.gnu.org/archive/html/lilypond-devel/2021-09/msg00048.html). 
Is there any reason not to introduce a model in which the arpeggio 
glyphs are upright from the start?

Thanks in advance for your time,
Owen Lamb