Thanks for your comments. I will make more comments about "wght" and "wdth" on Peter's 1.8.2 thread soon. But, the two systems (TN's proposal, and the 1.8.2 spec of width and weight axes), can only be automated one way. So, I don't believe:
"A conversion of "wght" into a system like the TN proposal can be fully automated".
If I understand the spec, to be brief, all of the instances of the "regular" weight, must have a weight value of 400. There are thousands of such regular instances in Amstelvar, (sizes, widths and grades of regular), and I know, as they should, those instances have different weights, so they work as a family of typefaces in typography at all those different sizes, widths and grades of regular.
Removing all the other Amstelvar axes from consideration, I am to label all of Amstelvar's Regulars with 400 wght. This is a simple enough post-process, (as the current wght is per mille, I think), and an “easy fix" for customers who need it. But I couldn’t take a 3 axes variable font, like Amstelvar, where all those Regulars have been labeled "400", and do any more automation with them. I could be wrong but that is not an easy fix.