There is already a perfectly good technical term for this kind of thing: Metafont, coined by Donald Knuth in 1979. (The classical Greek prefix meaning “beyond”—hence Metafont would cover both “restricted” and “unrestricted” implementations.) But every organization wants to put its own brand on the concept, hence Multiple Masters, GX and now Variable. So don’t kid me that “Variable” is anything other than a snappy marketing term!
A “sans-serif text face” doesn’t mean much. That’s like saying a leather foot shoe. All alphabetic typefaces are potentially “great for reading”. It’s how they’re chosen and set for a particular document that’s significant.
nb, “text” has a specific typographic meaning (think “text” as Unicode strings, as opposed to graphics files), “text faces” is an indiscriminate, vernacular usage, like calling typefaces fonts, because all faces with alphabets are text faces (as opposed to symbol faces).