Quoted from Aurich:

It applies, units in Illustrator aren't actually a fixed concept, you can switch between them at will, they won't change the SVG scaling. Let me show you. This Illustrator file was set to inches, and I exported an SVG with the following dimensions:
[quoted image]
Then I opened it in Carbide Create, a program for exporting tool paths to a CNC. So perfect example of taking someone's Illustrator file and turning it into cut paths to make say a slingshot or ball trough or inserts etc.
This is what Carbide Create shows me on importing that file:
[quoted image]
As you can see it's off by the exact same scale factor discussed. 96/72=1.33 and 10/7.5=1.33
I can correct for that if I know to look for it, but just importing someone else's SVG I'll have no clue. Which is why if this idea takes off I don't recommend using SVG as a format. It's an unfortunate issue Adobe refuses to fix because they don't want to break backwards compatibility.

Quoted from Aurich:

The problem is .svg is a generic format, and you don't know what program created it. So it might have been made in Inkscape and be the right size, but you thought it was from Illustrator and make it 33% bigger and it doesn't fit.
This is why Adobe really should just get over themselves and fix it.
That said, it would be smart to include dimensions for things so that people could sanity check. Annnnnd, that's how this all starts getting complicated.

Quoted from Aurich:

STL is for 3D objects, we're discussing 2D ones, like laser cutting playfield protectors, which is what this thread was started about.
This is honestly kind of a huge undertaking because there are so many different formats and things people might want to archive.