This reminds me a little of Prototypo.
That's not going to solve the load problem. 3 weights are already considered moderate loading time by google fonts. You'd need 4 weights just to have a roman and an italic. Of course you could have any weight you want but it doesn't help mixing font styles.
A major reason for that, though, is that all four of those weights represent a separate network request, even if only for a word or two. This could severely reduce that particular impact of web fonts.
You’re not understanding the thing right. You could load 2 OT Var font files to the webpage (one upright, one italic) and then you can have any weight you want by specifying it in CSS.
LONG LIVE MULTIPLE MASTER